Category: 11. Java.lang Package

Introduction

The Java InheritableThreadLocal class extends ThreadLocal to provide inheritance of values from parent thread to child thread: when a child thread is created, the child receives initial values for all inheritable thread-local variables for which the parent has values.

Class Declaration

Following is the declaration for java.lang.InheritableThreadLocal class −

publicclassInheritableThreadLocal<T>extendsThreadLocal<T>

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Class constructors

Class methods

Methods inherited

This class inherits methods from the following classes −

• java.lang.ThreadLocal
• java.lang.Object

Introduction

The Java Float class wraps a value of primitive type float in an object. An object of type Float contains a single field whose type is float.

Class Declaration

Following is the declaration for java.lang.Float class −

publicfinalclassFloatextendsNumberimplementsComparable<Float>

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Field

Following are the fields for java.lang.Float class −

• static int MAX_EXPONENT − This is Maximum exponent a finite float variable may have.
• static float MAX_VALUE − This is a constant holding the largest positive finite value of type float, (2-2-²³)·2¹²⁷.
• static int MIN_EXPONENT − This is minimum exponent a normalized float variable may have.
• static float MIN_NORMAL − This is a constant holding the smallest positive normal value of type float, 2-¹²⁶.
• static float MIN_VALUE − This is a constant holding the smallest positive nonzero value of type float, 2-¹⁴⁹.
• static float NaN − This is a constant holding a Not-a-Number (NaN) value of type float.
• static float NEGATIVE_INFINITY − This is a constant holding the negative infinity of type float.
• static float POSITIVE_INFINITY − This is a constant holding the positive infinity of type float.
• static int SIZE − This is the number of bits used to represent a float value.
• static Class<Float> TYPE − This is the Class instance representing the primitive type float.

Class constructors

Class methods

Methods inherited

This class inherits methods from the following classes −

• java.lang.Object

Example

The following example shows the usage of Float class to get float from a string.

Open Compiler

packagecom.tutorialspoint;publicclassFloatDemo{publicstaticvoidmain(String[] args){// create a String s and assign value to itString s ="+120";// create a Float object fFloat f;// get the value of float from string
  f =Float.valueOf(s);// print the valueSystem.out.println("Float value of string "+ s +" is "+ f );}}</code></pre>


Let us compile and run the above program, this will produce the following result −



Float value of string +120 is 120.0

Introduction

The Java Enum class is the common base class of all Java language enumeration types.

Class Declaration

Following is the declaration for java.lang.Enum class −

publicabstractclassEnum<E extends Enum<E>>extendsObjectimplementsComparable<E>,Serializable

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Class constructors

Class methods

Methods inherited

This class inherits methods from the following classes −

• java.lang.Object

Example

Following example showcases the usage of enum in if and switch statements.

Open Compiler

packagecom.tutorialspoint;publicclassEnumDemo{publicstaticvoidmain(String args[]){//print an EnumSystem.out.println(Mobile.Motorola);Mobile mobile =Mobile.Samsung;//Usage in IF statmentif(mobile ==Mobile.Samsung){System.out.println("Matched");}//Usage in Swith statmentswitch(mobile){caseSamsung:System.out.println("Samsung");break;caseNokia:System.out.println("Nokia");break;caseMotorola:System.out.println("Motorola");}}}enumMobile{Samsung,Nokia,Motorola}

Output

Let us compile and run the above program, this will produce the following result −

Motorola
Matched
Samsung

Introduction

The Java Double class wraps a value of primitive type double in an object. An object of type Double contains a single field whose type is double.

Class Declaration

Following is the declaration for java.lang.Double class −

publicfinalclassDoubleextendsNumberimplementsComparable<Double>

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Field

Following are the fields for java.lang.Double class −

• static int MAX_EXPONENT − This is the maximum exponent a finite double variable may have.
• static double MAX_VALUE − This is the constant holding the largest positive finite value of type double, (2-2-⁵²)×2¹⁰²³.
• static int MIN_EXPONENT − This is the minimum exponent a normalized double variable may have.
• static double MIN_NORMAL − This is the constant holding the smallest positive normal value of type double, 2^-1022.
• static double MIN_VALUE − This is the constant holding the smallest positive nonzero value of type double, 2^-1074.
• static double NaN − This is the constant holding a Not-a-Number (NaN) value of type double.
• static double NEGATIVE_INFINITY − This is the constant holding the negative infinity of type double.
• static double POSITIVE_INFINITY − This is the constant holding the positive infinity of type double.
• static int SIZE − This is the number of bits used to represent a double value.
• static Class<Double> TYPE − This is the class instance representing the primitive type double

Class constructors

Class methods

Methods inherited

This class inherits methods from the following classes −

• java.lang.Object

Example

The following example shows the usage of Double class to get double from a string. We’ve created a String and then using valueOf() method, we’re retrieving getting a Double Object and then double object is printed.

Open Compiler

packagecom.tutorialspoint;publicclassDoubleDemo{publicstaticvoidmain(String[] args){// create a String s and assign value to itString s ="+120";// create a Double object bDouble b;// get the value of double from string
  b =Double.valueOf(s);// print b valueSystem.out.println("Double value of string "+ s +" is "+ b );}}</code></pre>


Output



Let us compile and run the above program, this will produce the following result −



Double value of string +120 is 120.0

Introduction

The Java Compiler class is provided to support Java-to-native-code compilers and related services. By design, it serves as a placeholder for a JIT compiler implementation.

Note − This API is deprecated since Java 9 and is not available Java 21 onwards.

Class Declaration

Following is the declaration for java.lang.Compiler class −

publicfinalclassCompilerextendsObject

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Class methods

Methods inherited

This class inherits methods from the following classes −

• java.lang.Object

Enabling a Compiler Example

The following example shows the usage of java.lang.Compiler.enable() method. In this program, we’ve enabled the compiler using enable() method. Then prepare a compile command using command() method. Then we’ve retrieved hashcode of a new Integer object created and printed the same.

packagecom.tutorialspoint;publicclassCompilerDemo{publicstaticvoidmain(String[] args){// checking if compiler is enabled or not        Compiler.enable();System.out.println("Compiler Enabled...");Compiler.command("{java.lang.Integer.*}(compile)");Integer i =newInteger("50");// returns a hash code valueint retval = i.hashCode();System.out.println("Value = "+ retval);}}

Output

Let us compile and run the above program, this will produce the following result −

Compiler Enabled...
Value = 50

Introduction

The Java ClassLoader class is an object that is responsible for loading classes. This class is an abstract class. It may be used by security managers to indicate security domains.

Class Declaration

Following is the declaration for java.lang.ClassLoader class −

publicabstractclassClassLoaderextendsObject

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Class constructors

Class methods

Methods inherited

This class inherits methods from the following classes −

• java.lang.Object

Getting ClassLoader and its Parent ClassLoader Example

The following example shows the usage of java.lang.ClassLoader.getParent() method. In this program, we’ve retrieved class of a ClassLoaderDemo. Then using getClassLoader(), we get the required ClassLoader and printed class loader class using getClass() and printed the parent class loader using getParent() method.

Open Compiler

packagecom.tutorialspoint;publicclassClassLoaderDemo{publicstaticvoidmain(String[] args)throwsException{Class cls =Class.forName("com.tutorialspoint.ClassLoaderDemo");// returns the ClassLoader object associated with this ClassClassLoader cLoader = cls.getClassLoader();System.out.println(cLoader.getClass());// returns the parent ClassLoaderSystem.out.println(cLoader.getParent());}}

Output

Let us compile and run the above program, this will produce the following result −

class jdk.internal.loader.ClassLoaders$AppClassLoader
jdk.internal.loader.ClassLoaders$PlatformClassLoader@4517d9a3

Introduction

The Java Class class instance represent classes and interfaces in a running Java application. It has no public constructor.

Class Declaration

Following is the declaration for java.lang.Class class −

publicfinalclassClass<T>extendsObjectimplementsSerializable,GenericDeclaration,Type,AnnotatedElement

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Class methods

Methods inherited

This class inherits methods from the following classes −

• java.lang.Object

Getting Class Names and Casting a Parent Class as SubClass Example

The following example shows the usage of Class asSubclass() method. We’ve created two classes, ClassDemo and its subclass SubClass1. Using getClass() method, we printed the class names and then using asSubClass we’re casting parent class as child class and are getting its instance.

Open Compiler

packagecom.tutorialspoint;publicclassClassDemo{publicstaticvoidmain(String[] args){try{ClassDemo cls =newClassDemo();ClassDemo subcls =newSubClass1();// class ClassDemoClass c = cls.getClass();System.out.println(c);// sub class SubClass1Class c1 = subcls.getClass();System.out.println(c1);// represent a subclass of the specified class objectClass retval = c1.asSubclass(c);System.out.println(retval);}catch(ClassCastException e){System.out.println(e.toString());}}}classSubClass1extendsClassDemo{// sub class}

Let us compile and run the above program, this will produce the following result −

class com.tutorialspoint.ClassDemo
class com.tutorialspoint.SubClass1
class com.tutorialspoint.SubClass1