Mutable and Immutable Classes in JAVA

7/31/2019 Mutable and Immutable Classes in JAVA

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Mutable and

immutableclasses


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AGENDA

Introduction

Mutable Classes

Immutable Classes

Cloning and Mutable

Conclusion


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Introduction

An Immutable object is a kind of object whose

state cannot be modified after it is created where

a Mutable Object can be modified after it is

created.


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Immutable

A class that contains methods (other thanconstructors) that change any of the data in an

object of the class is called immutable classes

and object of the class are called immutable

objects.

Stringsare immutable class.

In Java, objects are referred by references.

If an object is known to be immutable, the

object reference can be shared.


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For example, Boolean, Byte, Character,

Double, Float, Integer, Long, Short, and Stringare immutable classes in Java.

An immutable object is one whose externally

visible state cannot change after it is

instantiated.

The String, Integer, and BigDecimal classes in

the Java class library are examples of

immutable objects -- they represent a singlevalue that cannot change over the lifetime of

the object.


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Sample Program

Class Pro1

{

public static void main(String[] args)

{

String str = "WELCOME";

System.out.println(str);

str.toLowerCase(); //Doesnt impact on original content ofStr

System.out.println(str); Output

} WELCOME

} WELCOME


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Modified Program

class Pro1

{

public static void main(String[] args)

{String str = WELCOME";

System.out.println(str);

String str1 = str.toLower();

System.out.println(str1); Output} WELCOME

} welcome


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Mutable

A class that contains public methods or inputmethods that can change the data in an object

of the class is called mutable classes and the object

of the class are called mutable objects.

The class Date is an example of a mutable class.

When defining any methods , that method should

not return a reference to a mutable object.

Instead use a copy constructor to return a

reference to a completely independent copy of

the mutable object.


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A String Buffer is a string that can be changed. StringBuffers are Mutable, theyre not inherently thread safe

and thus many of the methods of String Buffer class

are synchronized.

The StringBuffer has the methods

Append( )

Insert ( )


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Mutable Objects in AWT and Swing

Thejava.awt package defines several classes that encapsulategeometric information.

AWT Geometry Classes

CLASS DESCRIPTIONPoint (x , y) location in space

Dimension Component width and

height

Insets Representation of the

Borders of a container

Rectangle Area in a coordinate

space


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Thejava.awt.Component andjava.awt.Containerclasses define methods to access certain geometric

information.

public Point getLocation();

public void setLocation( Point loc);

public Dimension getSize();

public void setSize(Dimension size);

public Insets getInsets();

public void setInsets(Insets insets);

public Rectangle getBounds();

public void setBounds(Rectangle bounds);


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Cloning and mutable objects

All classes that implement Cloneable should override

clone with a public method whose return type is the

class itself.

This method should call super.clone and then fix any

fields that need to be fixed.

Typically this means copying any mutable objects

that comprise the internal deep structure of object

being cloned and replacing the clones references to

these objects with references to the copies.


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Reference

1. Absolute JAVA Walter Savitch

2. Effective Java Joshua Bloch

Websites

www.sun.com

www.google.com
http://www.sun.com/http://www.google.com/http://www.google.com/http://www.sun.com/


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Mutable and Immutable Classes in JAVA

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