This article shows you the difference between Mutable and Immutable objects in Java
1. Mutable object – You can change the states and fields after the object is created. For examples: StringBuilder, java.util.Date and etc.
2. Immutable object – You cannot change anything after the object is created. For examples: String, boxed primitive objects like Integer, Long and etc.
1. Java Mutable Example
Normally, it provides a method to modify the field value, and the object can be extended.
MutableExample.java
package com.mkyong;
public class MutableExample {
private String name;
MutableClass(String name) {
this.name = name;
}
public String getName() {
return name;
}
// this setter can modify the name
public void setName(String name) {
this.name = name;
}
public static void main(String[] args) {
MutableExample obj = new MutableExample("mkyong");
System.out.println(obj.getName());
// update the name, this object is mutable
obj.setName("new mkyong");
System.out.println(obj.getName());
}
}
Output
mkyong
new mkyong
2. Java Immutable Example
To create an Immutable object, make the class final, and don’t provide any methods to modify the fields.
ImmutableExample.java
package com.mkyong;
// make this class final, no one can extend this class
public final class ImmutableExample {
private String name;
ImmutableExample (String name) {
this.name = name;
}
public String getName() {
return name;
}
//no setter
public static void main(String[] args) {
ImmutableExample obj = new ImmutableExample("mkyong");
System.out.println(obj.getName());
// there is no way to update the name after the object is created.
// obj.setName("new mkyong");
// System.out.println(obj.getName());
}
}
Output
mkyong
Note
Immutable object is simple, thread-safe (no need synchronization), less prone to error and more secure. If possible, make all objects immutable.
Immutable object is simple, thread-safe (no need synchronization), less prone to error and more secure. If possible, make all objects immutable.
P.S Please refer to the Effective Java Book – Item 15: Minimize mutability.
It is not an exact example of the Immutable class construction, this example shows the use of Immutable
I’d like to suggest an edit.
In the MutableExample class, you have named the constructor – “MutableClass”, which should be “MutableExample” I believe, same as the class name.
the variable (i.e. name in class ImmutableExample ) must be final to make it immutable.
no setter is enough
I thing, Jagat is right.
Here in this example, you can update the value of the variable name.
obj. name = “Jagat”;
So the variable “name” must be made final.
super sir