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hashcode method in java


The hashCode() method in java is an Object class method. It returns a hash code value (an integer number) for the object which represents the memory address of the object. It is supported for the benefit of hashtables such as those provided by java.util.Hashtable.

The general contract of hashCode and equals is:

  • Whenever it is invoked on the same object more than once during an execution of a Java application, the hashCode method must consistently return the same integer, provided no information used in equals comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application.
  • If two objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result.
  • It is not required that if two objects are unequal according to the equals(java.lang.Object) method, then calling the hashCode method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hashtables.

 

Java hashCode method example

package com.codesjava;
 
public class Test {
	public static void main(String args[]){
		String str1 = "codesjava";
		String str2 = "codesjava";
		//Will generate same hash code
		System.out.println(str1.hashCode());
		System.out.println(str2.hashCode());
 
		String str3 = new String("codesjava");
		String str4 = new String("codesjava");
		//Will generate same hash code
		System.out.println(str3.hashCode());
		System.out.println(str4.hashCode());
 
		Site site1 = new Site("codesjava", 1);
		Site site2 = new Site("codesjava", 1);
		//Will generate different hash code
		System.out.println(site1.hashCode());
		System.out.println(site2.hashCode());		
	}
}
 
class Site{
	private String name;
	private int id;
 
	public Site(String name, int id) {
		super();
		this.name = name;
		this.id = id;
	}
 
	public String getName() {
		return name;
	}
 
	public void setName(String name) {
		this.name = name;
	}
 
	public int getId() {
		return id;
	}
 
	public void setId(int id) {
		this.id = id;
	}	
}

Output

-1108854968
-1108854968
-1108854968
-1108854968
366712642
1829164700

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