Category: Tutorials

/**
@author Larry Battle <bateru.com/news>
@date April 19, 2012
@purpose To show a simple comparison between == and equals().
*/
 
public class SameObjectTest {
	public static boolean areAssertsEnabled(){
		boolean isEnabled = false;
		try{
			assert false: "Yes asserts are enabled.";
		}catch( AssertionError e ){
			isEnabled = true;
		}
		return isEnabled;
	}
	public static void main(String[] args ){
		// All asserts should be without an error.
		String message = "Test Completed with no errors.";
		int[] ints = new int[]{ 10, 10, 20 };
		String[] strings = new String[]{ new String( "Duck" ), new String( "Duck" ), new String( "Goose!" ) };
		Worker[] workers = new Worker[]{ new Worker( "Working" ), new Worker( "Working" ), new Worker( "Sleeping" ) };
 
		assert ints[0] == ints[1] : "10 is 10";
		assert ints[1] != ints[2] : "10 is not 20";
		// Primative data types can't use ints[i].equals( ints[j] ) because they don't have methods.
 
		// Strings are a little bit more tricky. Go here for more inforamtion. http://www.janeg.ca/scjp/lang/strLiteral.html
		assert strings[0] == strings[0]: "An equality check, ==, on objects compares the references, not the values.";
		assert strings[0] != strings[1]: "strings[0] and strings[1] do not have the same reference point. In otherwords, that don't have the same Class and hashCodes.";
		assert strings[0].equals( strings[1] ): "String equals methods is predefined to compare the value of the string objects.";
		assert !strings[0].equals( strings[2] ): "the string duck should not equal the string goose!";
 
		// You have to override the equals methods for user-defined objects.
		assert workers[0] != workers[1]: "workers[0] and workers[1] have two different hash values.";
		assert workers[0].equals( workers[1] ): "However workers[0] and workers[1] are equivalent to eachother, according to the equals method.";
		assert !workers[1].equals( workers[2] ): "But this is not the case for workers[1] and workers[2].";
 
		message = ( areAssertsEnabled() ) ? message : "Asserts are disabled! Please enable with the switch -ea, ex. java -ea ";
		System.out.println( message );
	}
}
class Worker{
	public String status;
	public Worker( String status ){
		this.status = ( status != null ) ? status : "Unknown";
	}
	public boolean equals( Object obj ){
		boolean areSame = false;
		Worker x;
		if( obj != null  ){
			if( obj == this ){
				areSame = true;
			}
			if( this.getClass() == obj.getClass() ){
				x = (Worker) obj;
				if( x != null && x.status.equals( this.status ) ){
					areSame = true;
				}
			}
		}
		return areSame;
	}
}

/** @author Larry Battle <bateru.com/news> @date April 19, 2012 @purpose To show a simple comparison between == and equals(). */ public class SameObjectTest { public static boolean areAssertsEnabled(){ boolean isEnabled = false; try{ assert false: "Yes asserts are enabled."; }catch( AssertionError e ){ isEnabled = true; } return isEnabled; } public static void main(String[] args ){ // All asserts should be without an error. String message = "Test Completed with no errors."; int[] ints = new int[]{ 10, 10, 20 }; String[] strings = new String[]{ new String( "Duck" ), new String( "Duck" ), new String( "Goose!" ) }; Worker[] workers = new Worker[]{ new Worker( "Working" ), new Worker( "Working" ), new Worker( "Sleeping" ) }; assert ints[0] == ints[1] : "10 is 10"; assert ints[1] != ints[2] : "10 is not 20"; // Primative data types can't use ints[i].equals( ints[j] ) because they don't have methods. // Strings are a little bit more tricky. Go here for more inforamtion. http://www.janeg.ca/scjp/lang/strLiteral.html assert strings[0] == strings[0]: "An equality check, ==, on objects compares the references, not the values."; assert strings[0] != strings[1]: "strings[0] and strings[1] do not have the same reference point. In otherwords, that don't have the same Class and hashCodes."; assert strings[0].equals( strings[1] ): "String equals methods is predefined to compare the value of the string objects."; assert !strings[0].equals( strings[2] ): "the string duck should not equal the string goose!"; // You have to override the equals methods for user-defined objects. assert workers[0] != workers[1]: "workers[0] and workers[1] have two different hash values."; assert workers[0].equals( workers[1] ): "However workers[0] and workers[1] are equivalent to eachother, according to the equals method."; assert !workers[1].equals( workers[2] ): "But this is not the case for workers[1] and workers[2]."; message = ( areAssertsEnabled() ) ? message : "Asserts are disabled! Please enable with the switch -ea, ex. java -ea "; System.out.println( message ); } } class Worker{ public String status; public Worker( String status ){ this.status = ( status != null ) ? status : "Unknown"; } public boolean equals( Object obj ){ boolean areSame = false; Worker x; if( obj != null ){ if( obj == this ){ areSame = true; } if( this.getClass() == obj.getClass() ){ x = (Worker) obj; if( x != null && x.status.equals( this.status ) ){ areSame = true; } } } return areSame; } }