String and Object Comparison

Comparison operator

Equality Testing vs. Assignment

· The = = operator tests for equality:if (x = = 0) . . // if x equals zero

· The = operator assigns a value to a variable:

x = 0; // assign 0 to x · Don't confuse them.

String Comparison

· Don't use = = for strings!if (input = = "Y") // WRONG!!!

· Use equals method:if (input.equals("Y"))

· = = tests identity, equals tests equal contents

· Case insensitive test ("Y" or "y")if (input.equalsIgnoreCase("Y"))

public class StringExample{ // instance variables - replace the example below with your own private String name; private String nickname;

/** * Constructor for objects of class StringExample */ public StringExample() { // initialize instance variables name = "Robert"; nickname = name.substring(0,3); } public void displayNames() { if (nickname == "Rob")

{ System.out.println("The nickname is Rob");

} else

{ System.out.println("There is no nickname");

}}

Object Comparison· = = tests for identity, equals for identical content

Rectangle cerealBox = new Rectangle(5, 10, 20, 30);Rectangle oatmealBox = new Rectangle(5, 10, 20, 30);Rectangle r = cerealBox;

· cerealBox != oatmealBox, but cerealBox.equals(oatmealBox)

· cerealBox == r· Note: equals must be defined for the class

Object Comparison