LAST UPDATE: MARCH 6, 2015

 

http://www.javapractices.com/topic/TopicAction.do?Id=17

 

Please note that many IDEs offer generators for both equals() and hashCode():

 

The Eclipse IDE.

package org.bjornkrols.templates;

/**
 * @author 		Bjorn Krols (Botre)
 * @version		0.0
 * @since		March 6, 2015
 */

 public final class EqualsAndHashCodeTemplate {

	public boolean significantBoolean;
	public int significantInteger;
	
	private EqualsAndHashCodeTemplate() {
		// This class should never be instantiated.
		// Do not delete or make accessible.
	}
	
	@Override
	public int hashCode() {
		
		// Create an int "result" and assign a non-zero value.
		int result = 17;
		
		// Create an int "prime" and assign a prime value.
		int prime = 34;
		
		/*
		For every field tested in the equals-Method, calculate a hash code c by:
		If the field f is a boolean: calculate (f ? 0 : 1);
		If the field f is a byte, char, short or int: calculate (int)f;
		If the field f is a long: calculate (int)(f ^ (f >>> 32));
		If the field f is a float: calculate Float.floatToIntBits(f);
		If the field f is a double: calculate Double.doubleToLongBits(f) and handle the return value like every long value;
		If the field f is an object: Use the result of the hashCode() method or 0 if f == null;
		If the field f is an array: See every field as separate element and calculate the hash value in a recursive fashion and combine the values as described next.
		Combine the hash value c with result with: result = prime * result + c
		*/
		result = prime * result + (significantBoolean ? 0 : 1);
		result = prime * result + significantInteger;
		 
		return result;
	}
	
	@Override
	public boolean equals(Object object) {
		
		// Optimization for true object equality.
		if (object == this) {
			return true;
		}
		
		// Check if object is an instance of this class (returns false if object is null).
		if (!(object instanceof EqualsAndHashCodeTemplate)) {
			return false;
		}
		
		// Cast object for comparison (safe).
		EqualsAndHashCodeTemplate castedObject = (EqualsAndHashCodeTemplate) object;
		
		// Check if all significant fields are equal.
		if (castedObject.significantBoolean != this.significantBoolean) {
			return false;
		}
		if (castedObject.significantInteger != this.significantInteger) {
			return false;
		}
		
		return true;
	}
	
}

Edited March 6, 201510 yr by Botre

Botre4president

Updated