The Java comments are the statements in a program that are not executed by the compiler and interpreter.
Why do we use comments in a code?
Comments are used to make the program more readable by adding the details of the code.
It makes easy to maintain the code and to find the errors easily.
The comments can be used to provide information or explanation about the variable, method, class, or any statement.
It can also be used to prevent the execution of program code while testing the alternative code.
Types of Java Comments
There are three types of comments in Java.
Single Line Comment
Multi Line Comment
Documentation Comment
1) Java Single Line Comment
The single-line comment is used to comment only one line of the code. It is the widely used and easiest way of commenting the statements.
Single line comments starts with two forward slashes (//). Any text in front of // is not executed by Java.
Syntax:
//This is single line comment
Let’s use single line comment in a Java program.
CommentExample1.java
public class CommentExample1 {
public static void main(String[] args) {
int i=10; // i is a variable with value 10
System.out.println(i); //printing the variable i
}
}
Output:
10
2) Java Multi Line Comment
The multi-line comment is used to comment multiple lines of code. It can be used to explain a complex code snippet or to comment multiple lines of code at a time (as it will be difficult to use single-line comments there).
Multi-line comments are placed between /* and */. Any text between /* and */ is not executed by Java.
Syntax:
/*
This
is
multi line
comment
*/
Let’s use multi-line comment in a Java program.
CommentExample2.java
public class CommentExample2 {
public static void main(String[] args) {
/* Let's declare and
print variable in java. */
int i=10;
System.out.println(i);
/* float j = 5.9;
float k = 4.4;
System.out.println( j + k ); */
}
}
Output:
10
Note: Usually // is used for short comments and /* */ is used for longer comments.
3) Java Documentation Comment
Documentation comments are usually used to write large programs for a project or software application as it helps to create documentation API. These APIs are needed for reference, i.e., which classes, methods, arguments, etc., are used in the code.
To create documentation API, we need to use the javadoc tool. The documentation comments are placed between /** and */.
Syntax:
/**
*
*We can use various tags to depict the parameter
*or heading or author name
*We can also use HTML tags
*
*/
javadoc tags
Some of the commonly used tags in documentation comments:
Tag
Syntax
Description
{@docRoot}
{@docRoot}
to depict relative path to root directory of generated document from any page.
@author
@author name – text
To add the author of the class.
@code
{@code text}
To show the text in code font without interpreting it as html markup or nested javadoc tag.
@version
@version version-text
To specify “Version” subheading and version-text when -version option is used.
@since
@since release
To add “Since” heading with since text to generated documentation.
@param
@param parameter-name description
To add a parameter with given name and description to ‘Parameters’ section.
@return
@return description
Required for every method that returns something (except void)
Let’s use the Javadoc tag in a Java program.
Calculate.java
import java.io.*;
/**
* <h2> Calculation of numbers </h2>
* This program implements an application
* to perform operation such as addition of numbers
* and print the result
* <p>
* <b>Note:</b> Comments make the code readable and
* easy to understand.
*
* @author Anurati
* @version 16.0
* @since 2021-07-06
*/
public class Calculate{
/**
* This method calculates the summation of two integers.
* @param input1 This is the first parameter to sum() method
* @param input2 This is the second parameter to the sum() method.
* @return int This returns the addition of input1 and input2
*/
public int sum(int input1, int input2){
return input1 + input2;
}
/**
* This is the main method uses of sum() method.
* @param args Unused
* @see IOException
*/
public static void main(String[] args) {
Calculate obj = new Calculate();
int result = obj.sum(40, 20);
System.out.println("Addition of numbers: " + result);
}
}
Compile it by javac tool:
Create Document
Create documentation API by javadoc tool:
Now, the HTML files are created for the Calculate class in the current directory, i.e., abcDemo. Open the HTML files, and we can see the explanation of Calculate class provided through the documentation comment.
Are Java comments executable?
Ans: As we know, Java comments are not executed by the compiler or interpreter, however, before the lexical transformation of code in compiler, contents of the code are encoded into ASCII in order to make the processing easy.
Test.java
public class Test{
public static void main(String[] args) {
//the below comment will be executed
// \u000d System.out.println("Java comment is executed!!");
}
}
Output:
The above code generate the output because the compiler parses the Unicode character \u000d as a new line before the lexical transformation, and thus the code is transformed as shown below:
Test.java
public class Test{
public static void main(String[] args) {
//the below comment will be executed
//
System.out.println("Java comment is executed!!");
}
}
The continue statement is used in loop control structure when you need to jump to the next iteration of the loop immediately. It can be used with for loop or while loop.
The Java continue statement is used to continue the loop. It continues the current flow of the program and skips the remaining code at the specified condition. In case of an inner loop, it continues the inner loop only.
We can use Java continue statement in all types of loops such as for loop, while loop and do-while loop.
Syntax:
jump-statement;
continue;
Java Continue Statement Example
ContinueExample.java
//Java Program to demonstrate the use of continue statement
//inside the for loop.
public class ContinueExample {
public static void main(String[] args) {
//for loop
for(int i=1;i<=10;i++){
if(i==5){
//using continue statement
continue;//it will skip the rest statement
}
System.out.println(i);
}
}
}
Output:
1
2
3
4
6
7
8
9
10
As you can see in the above output, 5 is not printed on the console. It is because the loop is continued when it reaches to 5.
Java Continue Statement with Inner Loop
It continues inner loop only if you use the continue statement inside the inner loop.
ContinueExample2.java
//Java Program to illustrate the use of continue statement
//inside an inner loop
public class ContinueExample2 {
public static void main(String[] args) {
//outer loop
for(int i=1;i<=3;i++){
//inner loop
for(int j=1;j<=3;j++){
if(i==2&&j==2){
//using continue statement inside inner loop
continue;
}
System.out.println(i+" "+j);
}
}
}
}
Output:
1 1
1 2
1 3
2 1
2 3
3 1
3 2
3 3
Java Continue Statement with Labelled For Loop
We can use continue statement with a label. This feature is introduced since JDK 1.5. So, we can continue any loop in Java now whether it is outer loop or inner.
Example:
ContinueExample3.java
//Java Program to illustrate the use of continue statement
//with label inside an inner loop to continue outer loop
public class ContinueExample3 {
public static void main(String[] args) {
aa:
for(int i=1;i<=3;i++){
bb:
for(int j=1;j<=3;j++){
if(i==2&&j==2){
//using continue statement with label
continue aa;
}
System.out.println(i+" "+j);
}
}
}
}
Output:
1 1
1 2
1 3
2 1
3 1
3 2
3 3
Java Continue Statement in while loop
ContinueWhileExample.java
//Java Program to demonstrate the use of continue statement
//inside the while loop.
public class ContinueWhileExample {
public static void main(String[] args) {
//while loop
int i=1;
while(i<=10){
if(i==5){
//using continue statement
i++;
continue;//it will skip the rest statement
}
System.out.println(i);
i++;
}
}
}
Output:
1
2
3
4
6
7
8
9
10
Java Continue Statement in do-while Loop
ContinueDoWhileExample.java
//Java Program to demonstrate the use of continue statement
//inside the Java do-while loop.
public class ContinueDoWhileExample {
public static void main(String[] args) {
//declaring variable
int i=1;
//do-while loop
do{
if(i==5){
//using continue statement
i++;
continue;//it will skip the rest statement
}
System.out.println(i);
i++;
}while(i<=10);
}
}
When a break statement is encountered inside a loop, the loop is immediately terminated and the program control resumes at the next statement following the loop.
The Java break statement is used to break loop or switch statement. It breaks the current flow of the program at specified condition. In case of inner loop, it breaks only inner loop.
We can use Java break statement in all types of loops such as for loop, while loop and do-while loop.
Syntax:
jump-statement;
break;
Flowchart of Break Statement
Java Break Statement with Loop
Example:
BreakExample.java
//Java Program to demonstrate the use of break statement
//inside the for loop.
public class BreakExample {
public static void main(String[] args) {
//using for loop
for(int i=1;i<=10;i++){
if(i==5){
//breaking the loop
break;
}
System.out.println(i);
}
}
}
Output:
1
2
3
4
Java Break Statement with Inner Loop
It breaks inner loop only if you use break statement inside the inner loop.
Example:
BreakExample2.java
//Java Program to illustrate the use of break statement
//inside an inner loop
public class BreakExample2 {
public static void main(String[] args) {
//outer loop
for(int i=1;i<=3;i++){
//inner loop
for(int j=1;j<=3;j++){
if(i==2&&j==2){
//using break statement inside the inner loop
break;
}
System.out.println(i+" "+j);
}
}
}
}
Output:
1 1
1 2
1 3
2 1
3 1
3 2
3 3
Java Break Statement with Labeled For Loop
We can use break statement with a label. The feature is introduced since JDK 1.5. So, we can break any loop in Java now whether it is outer or inner loop.
Example:
BreakExample3.java
//Java Program to illustrate the use of continue statement
//with label inside an inner loop to break outer loop
public class BreakExample3 {
public static void main(String[] args) {
aa:
for(int i=1;i<=3;i++){
bb:
for(int j=1;j<=3;j++){
if(i==2&&j==2){
//using break statement with label
break aa;
}
System.out.println(i+" "+j);
}
}
}
}
Output:
1 1
1 2
1 3
2 1
Java Break Statement in while loop
Example:
BreakWhileExample.java
//Java Program to demonstrate the use of break statement
//inside the while loop.
public class BreakWhileExample {
public static void main(String[] args) {
//while loop
int i=1;
while(i<=10){
if(i==5){
//using break statement
i++;
break;//it will break the loop
}
System.out.println(i);
i++;
}
}
}
Output:
1
2
3
4
Java Break Statement in do-while loop
Example:
BreakDoWhileExample.java
//Java Program to demonstrate the use of break statement
//inside the Java do-while loop.
public class BreakDoWhileExample {
public static void main(String[] args) {
//declaring variable
int i=1;
//do-while loop
do{
if(i==5){
//using break statement
i++;
break;//it will break the loop
}
System.out.println(i);
i++;
}while(i<=10);
}
}
The Java do-while loop is used to iterate a part of the program repeatedly, until the specified condition is true. If the number of iteration is not fixed and you must have to execute the loop at least once, it is recommended to use a do-while loop.
Java do-while loop is called an exit control loop. Therefore, unlike while loop and for loop, the do-while check the condition at the end of loop body. The Java do-while loop is executed at least once because condition is checked after loop body.
Syntax:
do{
//code to be executed / loop body
//update statement
}while (condition);
The different parts of do-while loop:
1. Condition: It is an expression which is tested. If the condition is true, the loop body is executed and control goes to update expression. As soon as the condition becomes false, loop breaks automatically.
Example:
i <=100
2. Update expression: Every time the loop body is executed, the this expression increments or decrements loop variable.
Example:
i++;
Note: The do block is executed at least once, even if the condition is false.
Flowchart of do-while loop:
Example:
In the below example, we print integer values from 1 to 10. Unlike the for loop, we separately need to initialize and increment the variable used in the condition (here, i). Otherwise, the loop will execute infinitely.
DoWhileExample.java
public class DoWhileExample {
public static void main(String[] args) {
int i=1;
do{
System.out.println(i);
i++;
}while(i<=10);
}
}
Output:
1
2
3
4
5
6
7
8
9
10
Java Infinitive do-while Loop
If you pass true in the do-while loop, it will be infinitive do-while loop.
Syntax:
do{
//code to be executed
}while(true);
Example:
DoWhileExample2.java
public class DoWhileExample2 {
public static void main(String[] args) {
do{
System.out.println("infinitive do while loop");
}while(true);
}
}
Output:
infinitive do while loop
infinitive do while loop
infinitive do while loop
ctrl+c
The Java while loop is used to iterate a part of the program repeatedly until the specified Boolean condition is true. As soon as the Boolean condition becomes false, the loop automatically stops.
The while loop is considered as a repeating if statement. If the number of iteration is not fixed, it is recommended to use the while loop.
Syntax:
while (condition){
//code to be executed
I ncrement / decrement statement
}
The different parts of do-while loop:
1. Condition: It is an expression which is tested. If the condition is true, the loop body is executed and control goes to update expression. When the condition becomes false, we exit the while loop.
Example:
i <=100
2. Update expression: Every time the loop body is executed, this expression increments or decrements loop variable.
Example:
i++;
Flowchart of Java While Loop
Here, the important thing about while loop is that, sometimes it may not even execute. If the condition to be tested results into false, the loop body is skipped and first statement after the while loop will be executed.
Example:
In the below example, we print integer values from 1 to 10. Unlike the for loop, we separately need to initialize and increment the variable used in the condition (here, i). Otherwise, the loop will execute infinitely.
WhileExample.java
public class WhileExample {
public static void main(String[] args) {
int i=1;
while(i<=10){
System.out.println(i);
i++;
}
}
}
Output:
1
2
3
4
5
6
7
8
9
10
Java Infinitive While Loop
If you pass true in the while loop, it will be infinitive while loop.
Syntax:
while(true){
//code to be executed
}
Example:
WhileExample2.java
public class WhileExample2 {
public static void main(String[] args) {
// setting the infinite while loop by passing true to the condition
while(true){
System.out.println("infinitive while loop");
}
}
}
Output:
infinitive while loop
infinitive while loop
infinitive while loop
infinitive while loop
infinitive while loop
ctrl+c
In the above code, we need to enter Ctrl + C command to terminate the infinite loop.
The Java for loop is used to iterate a part of the program several times. If the number of iteration is fixed, it is recommended to use for loop.
There are three types of for loops in Java.
Simple for Loop
For-each or Enhanced for Loop
Labeled for Loop
Java Simple for Loop
A simple for loop is the same as C/C++. We can initialize the variable, check condition and increment/decrement value. It consists of four parts:
Initialization: It is the initial condition which is executed once when the loop starts. Here, we can initialize the variable, or we can use an already initialized variable. It is an optional condition.
Condition: It is the second condition which is executed each time to test the condition of the loop. It continues execution until the condition is false. It must return boolean value either true or false. It is an optional condition.
Increment/Decrement: It increments or decrements the variable value. It is an optional condition.
Statement: The statement of the loop is executed each time until the second condition is false.
Syntax:
for(initialization; condition; increment/decrement){
//statement or code to be executed
}
Flowchart:
Example:
ForExample.java
//Java Program to demonstrate the example of for loop
//which prints table of 1
public class ForExample {
public static void main(String[] args) {
//Code of Java for loop
for(int i=1;i<=10;i++){
System.out.println(i);
}
}
}
Output:
1
2
3
4
5
6
7
8
9
10
Java Nested for Loop
If we have a for loop inside the another loop, it is known as nested for loop. The inner loop executes completely whenever outer loop executes.
Example:
NestedForExample.java
public class NestedForExample {
public static void main(String[] args) {
//loop of i
for(int i=1;i<=3;i++){
//loop of j
for(int j=1;j<=3;j++){
System.out.println(i+" "+j);
}//end of i
}//end of j
}
}
Output:
1 1
1 2
1 3
2 1
2 2
2 3
3 1
3 2
3 3
Pyramid Example 1:
PyramidExample.java
public class PyramidExample {
public static void main(String[] args) {
for(int i=1;i<=5;i++){
for(int j=1;j<=i;j++){
System.out.print("* ");
}
System.out.println();//new line
}
}
}
Output:
*
* *
* * *
* * * *
* * * * *
Pyramid Example 2:
PyramidExample2.java
public class PyramidExample2 {
public static void main(String[] args) {
int term=6;
for(int i=1;i<=term;i++){
for(int j=term;j>=i;j--){
System.out.print("* ");
}
System.out.println();//new line
}
}
}
Output:
* * * * * *
* * * * *
* * * *
* * *
* *
*
Java for-each Loop
The for-each loop is used to traverse array or collection in Java. It is easier to use than simple for loop because we don’t need to increment value and use subscript notation.
It works on the basis of elements and not the index. It returns element one by one in the defined variable.
Syntax:
for(data_type variable : array_name){
//code to be executed
}
Example:
ForEachExample.java
//Java For-each loop example which prints the
//elements of the array
public class ForEachExample {
public static void main(String[] args) {
//Declaring an array
int arr[]={12,23,44,56,78};
//Printing array using for-each loop
for(int i:arr){
System.out.println(i);
}
}
}
Output:
12
23
44
56
78
Java Labeled For Loop
We can have a name of each Java for loop. To do so, we use label before the for loop. It is useful while using the nested for loop as we can break/continue specific for loop.
Note: The break and continue keywords breaks or continues the innermost for loop respectively.
Syntax:
labelname:
for(initialization; condition; increment/decrement){
//code to be executed
}
Example:
LabeledForExample.java
//A Java program to demonstrate the use of labeled for loop
public class LabeledForExample {
public static void main(String[] args) {
//Using Label for outer and for loop
aa:
for(int i=1;i<=3;i++){
bb:
for(int j=1;j<=3;j++){
if(i==2&&j==2){
break aa;
}
System.out.println(i+" "+j);
}
}
}
}
Output:
1 1
1 2
1 3
2 1
If you use break bb;, it will break inner loop only which is the default behaviour of any loop.
LabeledForExample2.java
public class LabeledForExample2 {
public static void main(String[] args) {
aa:
for(int i=1;i<=3;i++){
bb:
for(int j=1;j<=3;j++){
if(i==2&&j==2){
break bb;
}
System.out.println(i+" "+j);
}
}
}
}
Output:
1 1
1 2
1 3
2 1
3 1
3 2
3 3
Java Infinitive for Loop
If you use two semicolons ;; in the for loop, it will be infinitive for loop.
Syntax:
for(;;){
//code to be executed
}
Example:
ForExample.java
//Java program to demonstrate the use of infinite for loop
//which prints an statement
public class ForExample {
public static void main(String[] args) {
//Using no condition in for loop
for(;;){
System.out.println("infinitive loop");
}
}
}
Now, you need to press ctrl+c to exit from the program.
Java for Loop vs while Loop vs do-while Loop
Comparison
for loop
while loop
do-while loop
Introduction
The Java for loop is a control flow statement that iterates a part of the programs multiple times.
The Java while loop is a control flow statement that executes a part of the programs repeatedly on the basis of given boolean condition.
The Java do while loop is a control flow statement that executes a part of the programs at least once and the further execution depends upon the given boolean condition.
When to use
If the number of iteration is fixed, it is recommended to use for loop.
If the number of iteration is not fixed, it is recommended to use while loop.
If the number of iteration is not fixed and you must have to execute the loop at least once, it is recommended to use the do-while loop.
Syntax
for(init;condition;incr/decr){ // code to be executed }
The Java switch statement executes one statement from multiple conditions. It is like if-else-if ladder statement. The switch statement works with byte, short, int, long, enum types, String and some wrapper types like Byte, Short, Int, and Long. Since Java 7, you can use strings in the switch statement.
In other words, the switch statement tests the equality of a variable against multiple values.
Points to Remember
There can be one or N number of case values for a switch expression.
The case value must be of switch expression type only. The case value must be literal or constant. It doesn’t allow variables.
The case values must be unique. In case of duplicate value, it renders compile-time error.
The Java switch expression must be of byte, short, int, long (with its Wrapper type), enums and string.
Each case statement can have a break statement which is optional. When control reaches to the break statement, it jumps the control after the switch expression. If a break statement is not found, it executes the next case.
The case value can have a default label which is optional.
Syntax:
itch(expression){
case value1:
//code to be executed;
break; //optional
case value2:
//code to be executed;
break; //optional
......
default:
code to be executed if all cases are not matched;
}
Flowchart of Switch Statement
Example:
SwitchExample.java
public class SwitchExample {
public static void main(String[] args) {
//Declaring a variable for switch expression
int number=20;
//Switch expression
switch(number){
//Case statements
case 10: System.out.println("10");
break;
case 20: System.out.println("20");
break;
case 30: System.out.println("30");
break;
//Default case statement
default:System.out.println("Not in 10, 20 or 30");
}
}
}
Output:
20
Finding Month Example:
SwitchMonthExample.javaHTML
//Java Program to demonstrate the example of Switch statement
//where we are printing month name for the given number
public class SwitchMonthExample {
public static void main(String[] args) {
//Specifying month number
int month=7;
String monthString="";
//Switch statement
switch(month){
//case statements within the switch block
case 1: monthString="1 - January";
break;
case 2: monthString="2 - February";
break;
case 3: monthString="3 - March";
break;
case 4: monthString="4 - April";
break;
case 5: monthString="5 - May";
break;
case 6: monthString="6 - June";
break;
case 7: monthString="7 - July";
break;
case 8: monthString="8 - August";
break;
case 9: monthString="9 - September";
break;
case 10: monthString="10 - October";
break;
case 11: monthString="11 - November";
break;
case 12: monthString="12 - December";
break;
default:System.out.println("Invalid Month!");
}
//Printing month of the given number
System.out.println(monthString);
}
}
Output:
7 - July
Program to check Vowel or Consonant:
If the character is A, E, I, O, or U, it is vowel otherwise consonant. It is not case-sensitive.
SwitchVowelExample.java
public class SwitchVowelExample {
public static void main(String[] args) {
char ch='O';
switch(ch)
{
case 'a':
System.out.println("Vowel");
break;
case 'e':
System.out.println("Vowel");
break;
case 'i':
System.out.println("Vowel");
break;
case 'o':
System.out.println("Vowel");
break;
case 'u':
System.out.println("Vowel");
break;
case 'A':
System.out.println("Vowel");
break;
case 'E':
System.out.println("Vowel");
break;
case 'I':
System.out.println("Vowel");
break;
case 'O':
System.out.println("Vowel");
break;
case 'U':
System.out.println("Vowel");
break;
default:
System.out.println("Consonant");
}
}
}
Output:
Vowel
Java Switch Statement is fall-through
The Java switch statement is fall-through. It means it executes all statements after the first match if a break statement is not present.
Example:
SwitchExample2.java
//Java Switch Example where we are omitting the
//break statement
public class SwitchExample2 {
public static void main(String[] args) {
int number=20;
//switch expression with int value
switch(number){
//switch cases without break statements
case 10: System.out.println("10");
case 20: System.out.println("20");
case 30: System.out.println("30");
default:System.out.println("Not in 10, 20 or 30");
}
}
}
Output:
20
30
Not in 10, 20 or 30
Java Switch Statement with String
Java allows us to use strings in switch expression since Java SE 7. The case statement should be string literal.
Example:
SwitchStringExample.java
//Java Program to demonstrate the use of Java Switch
//statement with String
public class SwitchStringExample {
public static void main(String[] args) {
//Declaring String variable
String levelString="Expert";
int level=0;
//Using String in Switch expression
switch(levelString){
//Using String Literal in Switch case
case "Beginner": level=1;
break;
case "Intermediate": level=2;
break;
case "Expert": level=3;
break;
default: level=0;
break;
}
System.out.println("Your Level is: "+level);
}
}
Output:
Your Level is: 3
Java Nested Switch Statement
We can use switch statement inside other switch statement in Java. It is known as nested switch statement.
Example:
NestedSwitchExample.java
//Java Program to demonstrate the use of Java Nested Switch
public class NestedSwitchExample {
public static void main(String args[])
{
//C - CSE, E - ECE, M - Mechanical
char branch = 'C';
int collegeYear = 4;
switch( collegeYear )
{
case 1:
System.out.println("English, Maths, Science");
break;
case 2:
switch( branch )
{
case 'C':
System.out.println("Operating System, Java, Data Structure");
break;
case 'E':
System.out.println("Micro processors, Logic switching theory");
break;
case 'M':
System.out.println("Drawing, Manufacturing Machines");
break;
}
break;
case 3:
switch( branch )
{
case 'C':
System.out.println("Computer Organization, MultiMedia");
break;
case 'E':
System.out.println("Fundamentals of Logic Design, Microelectronics");
break;
case 'M':
System.out.println("Internal Combustion Engines, Mechanical Vibration");
break;
}
break;
case 4:
switch( branch )
{
case 'C':
System.out.println("Data Communication and Networks, MultiMedia");
break;
case 'E':
System.out.println("Embedded System, Image Processing");
break;
case 'M':
System.out.println("Production Technology, Thermal Engineering");
break;
}
break;
}
}
}
Output:
Data Communication and Networks, MultiMedia
Java Enum in Switch Statement
Java allows us to use enum in switch statement. Java enum is a class that represent the group of constants. (immutable such as final variables). We use the keyword enum and put the constants in curly braces separated by comma.
Example:
JavaSwitchEnumExample.java
//Java Program to demonstrate the use of Enum
//in switch statement
public class JavaSwitchEnumExample {
public enum Day { Sun, Mon, Tue, Wed, Thu, Fri, Sat }
public static void main(String args[])
{
Day[] DayNow = Day.values();
for (Day Now : DayNow)
{
switch (Now)
{
case Sun:
System.out.println("Sunday");
break;
case Mon:
System.out.println("Monday");
break;
case Tue:
System.out.println("Tuesday");
break;
case Wed:
System.out.println("Wednesday");
break;
case Thu:
System.out.println("Thursday");
break;
case Fri:
System.out.println("Friday");
break;
case Sat:
System.out.println("Saturday");
break;
}
}
}
}
Java allows us to use four wrapper classes: Byte, Short, Integer and Long in switch statement.
Example:
WrapperInSwitchCaseExample.java
//Java Program to demonstrate the use of Wrapper class
//in switch statement
public class WrapperInSwitchCaseExample {
public static void main(String args[])
{
Integer age = 18;
switch (age)
{
case (16):
System.out.println("You are under 18.");
break;
case (18):
System.out.println("You are eligible for vote.");
break;
case (65):
System.out.println("You are senior citizen.");
break;
default:
System.out.println("Please give the valid age.");
break;
}
}
}
The Java if statement is used to test the condition. It checks boolean condition: true or false. There are various types of if statement in Java.
if statement
if-else statement
if-else-if ladder
nested if statement
Java if Statement
The Java if statement tests the condition. It executes the if block if condition is true.
Syntax:
if(condition){
//code to be executed
}
Example:
//Java Program to demonstate the use of if statement.
public class IfExample {
public static void main(String[] args) {
//defining an 'age' variable
int age=20;
//checking the age
if(age>18){
System.out.print("Age is greater than 18");
}
}
}
Output:
Age is greater than 18
Java if-else Statement
The Java if-else statement also tests the condition. It executes the if block if condition is true otherwise else block is executed.
Syntax:
if(condition){
//code if condition is true
}else{
//code if condition is false
}
Example:
//A Java Program to demonstrate the use of if-else statement.
//It is a program of odd and even number.
public class IfElseExample {
public static void main(String[] args) {
//defining a variable
int number=13;
//Check if the number is divisible by 2 or not
if(number%2==0){
System.out.println("even number");
}else{
System.out.println("odd number");
}
}
}
Output:
odd number
Leap Year Example:
A year is leap, if it is divisible by 4 and 400. But, not by 100.
public class LeapYearExample {
public static void main(String[] args) {
int year=2020;
if(((year % 4 ==0) && (year % 100 !=0)) || (year % 400==0)){
System.out.println("LEAP YEAR");
}
else{
System.out.println("COMMON YEAR");
}
}
}
Output:
LEAP YEAR
Using Ternary Operator
We can also use ternary operator (? 🙂 to perform the task of if…else statement. It is a shorthand way to check the condition. If the condition is true, the result of ? is returned. But, if the condition is false, the result of : is returned.
Example:
public class IfElseTernaryExample {
public static void main(String[] args) {
int number=13;
//Using ternary operator
String output=(number%2==0)?"even number":"odd number";
System.out.println(output);
}
}
Output:
odd number
Java if-else-if ladder Statement
The if-else-if ladder statement executes one condition from multiple statements.
Syntax:
if(condition1){
//code to be executed if condition1 is true
}else if(condition2){
//code to be executed if condition2 is true
}
else if(condition3){
//code to be executed if condition3 is true
}
...
else{
//code to be executed if all the conditions are false
}
Example:
//Java Program to demonstrate the use of If else-if ladder.
//It is a program of grading system for fail, D grade, C grade, B grade, A grade and A+.
public class IfElseIfExample {
public static void main(String[] args) {
int marks=65;
if(marks<50){
System.out.println("fail");
}
else if(marks>=50 && marks<60){
System.out.println("D grade");
}
else if(marks>=60 && marks<70){
System.out.println("C grade");
}
else if(marks>=70 && marks<80){
System.out.println("B grade");
}
else if(marks>=80 && marks<90){
System.out.println("A grade");
}else if(marks>=90 && marks<100){
System.out.println("A+ grade");
}else{
System.out.println("Invalid!");
}
}
}
Output:
C grade
Program to check POSITIVE, NEGATIVE or ZERO:
public class PositiveNegativeExample {
public static void main(String[] args) {
int number=-13;
if(number>0){
System.out.println("POSITIVE");
}else if(number<0){
System.out.println("NEGATIVE");
}else{
System.out.println("ZERO");
}
}
}
Output:
NEGATIVE
Java Nested if statement
The nested if statement represents the if block within another if block. Here, the inner if block condition executes only when outer if block condition is true.
Syntax:
if(condition){
//code to be executed
if(condition){
//code to be executed
}
}
Example:
//Java Program to demonstrate the use of Nested If Statement.
public class JavaNestedIfExample {
public static void main(String[] args) {
//Creating two variables for age and weight
int age=20;
int weight=80;
//applying condition on age and weight
if(age>=18){
if(weight>50){
System.out.println("You are eligible to donate blood");
}
}
}}
Output:
You are eligible to donate blood
Example 2:
//Java Program to demonstrate the use of Nested If Statement.
public class JavaNestedIfExample2 {
public static void main(String[] args) {
//Creating two variables for age and weight
int age=25;
int weight=48;
//applying condition on age and weight
if(age>=18){
if(weight>50){
System.out.println("You are eligible to donate blood");
} else{
System.out.println("You are not eligible to donate blood");
}
} else{
System.out.println("Age must be greater than 18");
}
} }
Java compiler executes the code from top to bottom. The statements in the code are executed according to the order in which they appear. However, Java provides statements that can be used to control the flow of Java code. Such statements are called control flow statements. It is one of the fundamental features of Java, which provides a smooth flow of program.
Java provides three types of control flow statements.
Decision Making statements
if statements
switch statement
Loop statements
do while loop
while loop
for loop
for-each loop
Jump statements
break statement
continue statement
Decision-Making statements:
As the name suggests, decision-making statements decide which statement to execute and when. Decision-making statements evaluate the Boolean expression and control the program flow depending upon the result of the condition provided. There are two types of decision-making statements in Java, i.e., If statement and switch statement.
1) If Statement:
In Java, the “if” statement is used to evaluate a condition. The control of the program is diverted depending upon the specific condition. The condition of the If statement gives a Boolean value, either true or false. In Java, there are four types of if-statements given below.
Simple if statement
if-else statement
if-else-if ladder
Nested if-statement
Let’s understand the if-statements one by one.
1) Simple if statement:
It is the most basic statement among all control flow statements in Java. It evaluates a Boolean expression and enables the program to enter a block of code if the expression evaluates to true.
Syntax of if statement is given below.
if(condition) {
statement 1; //executes when condition is true
}
Consider the following example in which we have used the if statement in the java code.
Student.java
Student.java
public class Student {
public static void main(String[] args) {
int x = 10;
int y = 12;
if(x+y > 20) {
System.out.println("x + y is greater than 20");
}
}
}
Output:
x + y is greater than 20
2) if-else statement
The if-else statement is an extension to the if-statement, which uses another block of code, i.e., else block. The else block is executed if the condition of the if-block is evaluated as false.
Syntax:
if(condition) {
statement 1; //executes when condition is true
}
else{
statement 2; //executes when condition is false
}
Consider the following example.
Student.java
public class Student {
public static void main(String[] args) {
int x = 10;
int y = 12;
if(x+y < 10) {
System.out.println("x + y is less than 10");
} else {
System.out.println("x + y is greater than 20");
}
}
}
Output:
x + y is greater than 20
3) if-else-if ladder:
The if-else-if statement contains the if-statement followed by multiple else-if statements. In other words, we can say that it is the chain of if-else statements that create a decision tree where the program may enter in the block of code where the condition is true. We can also define an else statement at the end of the chain.
Syntax of if-else-if statement is given below.
if(condition 1) {
statement 1; //executes when condition 1 is true
}
else if(condition 2) {
statement 2; //executes when condition 2 is true
}
else {
statement 2; //executes when all the conditions are false
}
Consider the following example.
Student.java
public class Student {
public static void main(String[] args) {
String city = "Delhi";
if(city == "Meerut") {
System.out.println("city is meerut");
}else if (city == "Noida") {
System.out.println("city is noida");
}else if(city == "Agra") {
System.out.println("city is agra");
}else {
System.out.println(city);
}
}
}
Output:
Delhi
4. Nested if-statement
In nested if-statements, the if statement can contain a if or if-else statement inside another if or else-if statement.
Syntax of Nested if-statement is given below.
if(condition 1) {
statement 1; //executes when condition 1 is true
if(condition 2) {
statement 2; //executes when condition 2 is true
}
else{
statement 2; //executes when condition 2 is false
}
}
Consider the following example.
Student.java
public class Student {
public static void main(String[] args) {
String address = "Delhi, India";
if(address.endsWith("India")) {
if(address.contains("Meerut")) {
System.out.println("Your city is Meerut");
}else if(address.contains("Noida")) {
System.out.println("Your city is Noida");
}else {
System.out.println(address.split(",")[0]);
}
}else {
System.out.println("You are not living in India");
}
}
}
Output:
Delhi
Switch Statement:
In Java, Switch statements are similar to if-else-if statements. The switch statement contains multiple blocks of code called cases and a single case is executed based on the variable which is being switched. The switch statement is easier to use instead of if-else-if statements. It also enhances the readability of the program.
Points to be noted about switch statement:
The case variables can be int, short, byte, char, or enumeration. String type is also supported since version 7 of Java
Cases cannot be duplicate
Default statement is executed when any of the case doesn’t match the value of expression. It is optional.
Break statement terminates the switch block when the condition is satisfied. It is optional, if not used, next case is executed.
While using switch statements, we must notice that the case expression will be of the same type as the variable. However, it will also be a constant value.
The syntax to use the switch statement is given below.
switch (expression){
case value1:
statement1;
break;
.
.
.
case valueN:
statementN;
break;
default:
default statement;
}
Consider the following example to understand the flow of the switch statement.
Student.java
public class Student implements Cloneable {
public static void main(String[] args) {
int num = 2;
switch (num){
case 0:
System.out.println("number is 0");
break;
case 1:
System.out.println("number is 1");
break;
default:
System.out.println(num);
}
}
}
Output:
2
While using switch statements, we must notice that the case expression will be of the same type as the variable. However, it will also be a constant value. The switch permits only int, string, and Enum type variables to be used.
Loop Statements
In programming, sometimes we need to execute the block of code repeatedly while some condition evaluates to true. However, loop statements are used to execute the set of instructions in a repeated order. The execution of the set of instructions depends upon a particular condition.
In Java, we have three types of loops that execute similarly. However, there are differences in their syntax and condition checking time.
for loop
while loop
do-while loop
Let’s understand the loop statements one by one.
Java for loop
In Java, for loop is similar to C and C++. It enables us to initialize the loop variable, check the condition, and increment/decrement in a single line of code. We use the for loop only when we exactly know the number of times, we want to execute the block of code.
for(initialization, condition, increment/decrement) {
//block of statements
}
The flow chart for the for-loop is given below.
Consider the following example to understand the proper functioning of the for loop in java.
Calculation.java
public class Calculattion {
public static void main(String[] args) {
// TODO Auto-generated method stub
int sum = 0;
for(int j = 1; j<=10; j++) {
sum = sum + j;
}
System.out.println("The sum of first 10 natural numbers is " + sum);
}
}
Output:
The sum of first 10 natural numbers is 55
Java for-each loop
Java provides an enhanced for loop to traverse the data structures like array or collection. In the for-each loop, we don’t need to update the loop variable. The syntax to use the for-each loop in java is given below.
for(data_type var : array_name/collection_name){
//statements
}
Consider the following example to understand the functioning of the for-each loop in Java.
Calculation.java
public class Calculation {
public static void main(String[] args) {
// TODO Auto-generated method stub
String[] names = {"Java","C","C++","Python","JavaScript"};
System.out.println("Printing the content of the array names:\n");
for(String name:names) {
System.out.println(name);
}
}
}
Output:
Printing the content of the array names:
Java
C
C++
Python
JavaScript
Java while loop
The while loop is also used to iterate over the number of statements multiple times. However, if we don’t know the number of iterations in advance, it is recommended to use a while loop. Unlike for loop, the initialization and increment/decrement doesn’t take place inside the loop statement in while loop.
It is also known as the entry-controlled loop since the condition is checked at the start of the loop. If the condition is true, then the loop body will be executed; otherwise, the statements after the loop will be executed.
The syntax of the while loop is given below.
while(condition){
//looping statements
}
The flow chart for the while loop is given in the following image.
Consider the following example.
Calculation .java
public class Calculation {
public static void main(String[] args) {
// TODO Auto-generated method stub
int i = 0;
System.out.println("Printing the list of first 10 even numbers \n");
while(i<=10) {
System.out.println(i);
i = i + 2;
}
}
}
Output:
Printing the list of first 10 even numbers
0
2
4
6
8
10
Java do-while loop
The do-while loop checks the condition at the end of the loop after executing the loop statements. When the number of iteration is not known and we have to execute the loop at least once, we can use do-while loop.
It is also known as the exit-controlled loop since the condition is not checked in advance. The syntax of the do-while loop is given below.
do
{
//statements
} while (condition);
The flow chart of the do-while loop is given in the following image.
Consider the following example to understand the functioning of the do-while loop in Java.
Calculation.java
public class Calculation {
public static void main(String[] args) {
// TODO Auto-generated method stub
int i = 0;
System.out.println("Printing the list of first 10 even numbers \n");
do {
System.out.println(i);
i = i + 2;
}while(i<=10);
}
}
Output:
Printing the list of first 10 even numbers
0
2
4
6
8
10
Jump Statements
Jump statements are used to transfer the control of the program to the specific statements. In other words, jump statements transfer the execution control to the other part of the program. There are two types of jump statements in Java, i.e., break and continue.
Java break statement
As the name suggests, the break statement is used to break the current flow of the program and transfer the control to the next statement outside a loop or switch statement. However, it breaks only the inner loop in the case of the nested loop.
The break statement cannot be used independently in the Java program, i.e., it can only be written inside the loop or switch statement.
The break statement example with for loop
Consider the following example in which we have used the break statement with the for loop.
BreakExample.java
public class BreakExample {
public static void main(String[] args) {
// TODO Auto-generated method stub
for(int i = 0; i<= 10; i++) {
System.out.println(i);
if(i==6) {
break;
}
}
}
}
Output:
0
1
2
3
4
5
6
break statement example with labeled for loop
Calculation.java
public class Calculation {
public static void main(String[] args) {
// TODO Auto-generated method stub
a:
for(int i = 0; i<= 10; i++) {
b:
for(int j = 0; j<=15;j++) {
c:
for (int k = 0; k<=20; k++) {
System.out.println(k);
if(k==5) {
break a;
}
}
}
}
}
}
Output:
0
1
2
3
4
5
Java continue statement
Unlike break statement, the continue statement doesn’t break the loop, whereas, it skips the specific part of the loop and jumps to the next iteration of the loop immediately.
Consider the following example to understand the functioning of the continue statement in Java.
public class ContinueExample {
public static void main(String[] args) {
// TODO Auto-generated method stub
for(int i = 0; i<= 2; i++) {
for (int j = i; j<=5; j++) {
if(j == 4) {
continue;
}
System.out.println(j);
}
}
}
}
