AND Short Circuit Operator using Object as Parameters in Java

Question

public class TestPass {

int a,b;
TestPass(int i,int j)
{
    a=i;
    b=j;
}
boolean equals(TestPass o)
{
    if(o.a==a&&o.b==b)
        return true;
    else
        return false;
}

}

  class Test
  {
  public static void main(String[] args)  
  {
  TestPass ob1=new TestPass(100, 22);
  TestPass ob2=new TestPass(100, 23);


    System.out.println("Condition="+ob1.equals(ob2));
}

}

Output:

Condition=false

I cannot find the logic with this output,bcoz 'if(o.a==a&&o.b==b)' code is used AND short circuit operator(&&),it only checks left hand side of operator(i think so).

        TestPass ob1=new TestPass(100, 22);
        TestPass ob2=new TestPass(100, 23);

Here i gave different values,but i think AND short circuit operator(&&) only checks left hand side,my expected output is True!,I think i'm wrong.I need clarification, Expect your help.

" AND short circuit operator(&&),it only checks left hand side of operator(i think so)" <- Only if the left hand is false. See: https://stackoverflow.com/questions/9344305/what-is-short-circuiting-and-how-is-it-used-when-programming-in-java — OH GOD SPIDERS, Jun 13 '17 at 10:01
No `&&` checks the left hand side and if it is `true`, also checks the right hand side. If one or both of the sides are `false` , the whole expression yields `false`. — Arnaud, Jun 13 '17 at 10:01
If the `&&` operator only ever checked the left operand, what would ever be the point of supplying the right operand? — khelwood, Jun 13 '17 at 10:02
@OHGODSPIDERS If a == b is true, then c == d and e == f are never evaluated at all, again confused. — Enrique_Iglesias, Jun 13 '17 at 10:11
Whats the confusion? Short circuit evaluation will allways have the exact same result then it would have if all expressions get evaluated. Same end result with short circuit evaluation just in shorter time. It doesn't change the results of the evaluation. So if you really don't understand it just ignore that it's there and evaluate all conditions in your head ;) — OH GOD SPIDERS, Jun 13 '17 at 10:16

score 0 · Accepted Answer · answered Jun 13 '17 at 10:02

0

The short-circuit only applies if the left side is false. If the left side is true, it will go on to check the right-hand side.

In your case o.a==a is true, so it checks the right-hand side: o.b==b is false, making it false overall.

answered Jun 13 '17 at 10:02

stripybadger

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ΦXocę 웃 Пepeúpa ツ · Answer 2 · 2017-06-13T10:13:03.003

This is the rule about the short-circuit you need to keep in mind.

╔══════════╦════════════════════════════════════════════════════════════════════════╗
║ Operator ║                           short-circuit                                ║
╠══════════╬════════════════════════════════════════════════════════════════════════╣
║ A && B   ║ if A==false then the B expression is never evaluated                   ║
║ A || B   ║ if A==true then the B expression is never evaluated                    ║
╚══════════╩════════════════════════════════════════════════════════════════════════╝

score 0 · Answer 3 · answered Jun 13 '17 at 10:53

One way of thinking about it is to split the if-condition

boolean equals2(TestPass o) {
    if (o.a == a) {
        if (o.b == b) {
            return true;
        }
        return false;
    }
    return false;
}

or even

boolean equals3(TestPass o) {
    if (o.a == a) {
        return o.b == b;
    }
    return false;
}

FYI, your equals could be simplfied to return o.a==a&&o.b==b

AND Short Circuit Operator using Object as Parameters in Java

3 Answers3