Java - Character.Subset hashCode() Method

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The Java Character.Subset hashCode() method retrieves the standard hash code of the subset. A hash code is an integer value that represents a character or an input given to a hash function.

This method goes hand in hand with the Java Character.Subset equals() method as same subsets must have same hashcodes. However, vice versa is not valid; same hashcodes do not belong to the same subsets or inputs. Hence, the final keyword is used to maintain the consistency of both the methods.

Note − This method uses the inheritance concept to create a Subset object as the constructor in the Character.Subset class has protected access. Therefore, Character.Subset class is extended from another public class whose constructor uses super() method to invoke the Object class that creates an object.

Syntax

Following is the syntax for Java Character.Subset hashCode() method

public final int hashCode()

Parameters

This method does not accept any parameters.

Return Value

This method returns a hash code value for this object.

Example

The following example shows the usage of Java Character.Subset hashCode() method. Here, we instantiate CharacterSubsetDemo class objects with a String name as their values. Then, the hashcode() method is invoked on this object to obtain the hashcode of this object.

package com.tutorialspoint;
import java.lang.*;
public class CharacterSubsetDemo extends Character.Subset {
  
   // constructor of super class
   CharacterSubsetDemo(String s) {
      super(s); 
   }
   public static void main(String[] args) {
      CharacterSubsetDemo obj1 = new CharacterSubsetDemo("admin");
      CharacterSubsetDemo obj2 = new CharacterSubsetDemo("webmaster");
      CharacterSubsetDemo obj3 = new CharacterSubsetDemo("administrator");

      // returns a hash code value
      int retval = obj1.hashCode();
      System.out.println("Hash code of Object " + obj1 + " = " + retval);
      retval = obj2.hashCode();
      System.out.println("Hash code of Object " + obj2 + " = " + retval);
      retval = obj3.hashCode();
      System.out.println("Hash code of Object " + obj3 + " = " + retval);
   }
} 

Output

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

Hash code of Object admin = 1704856573
Hash code of Object webmaster = 705927765
Hash code of Object administrator = 366712642

Example

In the following example, we will instantiate two objects using the same input string and invoke the hashCode() method on the both objects. This method returns the hashcode of each object created.

import java.lang.*;
public class HashCodeDemo extends Character.Subset {
   HashCodeDemo(String s) {
      super(s);
   }
   public static void main(String []args){        
      HashCodeDemo obj = new HashCodeDemo("hello");        
      int h = obj.hashCode();
      System.out.println("Hashcode of the given object is " + h);        
      int h1 = obj.hashCode();
      System.out.println("Hashcode of the given object is " + h1);
   }
}

Output

The output for the program above after compiling and running is given as follows −

Hashcode of the given object is 705927765
Hashcode of the given object is 705927765

Example

In the example below, we will check if the two different objects with same object reference will have the same hashcode, generated by the invoking hashCode() method.

import java.lang.*;
public class HashCodeDemo extends Character.Subset {
   HashCodeDemo(String s) {
      super(s);
   }
   public static void main(String []args){        
      HashCodeDemo obj = new HashCodeDemo("admin");
      HashCodeDemo obj1 = obj;        
      boolean b = obj1.equals(obj);
      System.out.println(b);        
      int h = obj.hashCode();
      System.out.println("Hashcode of the given object is " + h);        
      int h1 = obj1.hashCode();
      System.out.println("Hashcode of the given object is " + h1);
   }
}

Output

Let us compile and run the program above, the output is achieved as follows −

true
Hashcode of the given object is 705927765
Hashcode of the given object is 705927765

Example

Suppose, the string name for the subset object is given as null, the following example shows how the hashCode() method works in such cases.

import java.lang.*;
public class HashCodeDemo extends Character.Subset {
   HashCodeDemo(String s) {
      super(s);
   }
   public static void main(String []args){        
      HashCodeDemo obj1 = new HashCodeDemo(null);        
      int h = obj1.hashCode();
      System.out.println("Hashcode of the given object is " + h);
   }
}

Exception

After compiling and executing the program above, the output displays a NullPointerException −

Exception in thread "main" java.lang.NullPointerException: nameat java.lang.Character$Subset.<init>(Character.java:615)
at HashCodeDemo.<init>(HashCodeDemo.java:6)
   at HashCodeDemo.main(HashCodeDemo.java:10)