Question

I just started learning Java and came across equals. After looking for the difference between equals and ==, I decided to practice it myself but I am not getting the expected results. here is the code:

public class Sandbox {

/**
 * @param args
 *
 */
private int a;
public void setAtta(int value){a=value;}
public int getAtta(){return a;}

public static void main(String[] args) {
    // TODO Auto-generated method stub
    Sandbox s = new Sandbox();
    s.setAtta(10);
    Sandbox s1 = new Sandbox();
    s1.setAtta(10);

    System.out.println(s==s1);//false- EXPECTED
    System.out.println(s.equals(s1));//false- I thought it should be true?


}

}

Answer 1

Object.equals in Java is equivalent to ==, i.e. it tests reference equality. Since your Sandbox class (implicitly) extends Object, and you don’t override equals, s.equals(s1) calls Object.equals.

To get the behaviour you want, add an equals method (override) to your class:

public boolean equals(Object obj) {
    if(this == obj) return true;
    if(!(obj instanceof Sandbox)) return false;
    Sandbox that = (Sandbox)obj;
    return this.a == that.a;
}