CODEWITHSUNDEEP
java
Paul
Paul

Reputation: 5223

How does Java deal with multiple conditions inside a single IF statement

Lets say I have this:

if(bool1 && bool2 && bool3) {
...
}

Now. Is Java smart enough to skip checking bool2 and bool3 if bool1 was evaluated to false? Does java even check them from left to right? I'm asking this because i was "sorting" the conditions inside my if statements by the time it takes to do them (starting with the cheapest ones on the left). Now I'm not sure if this gives me any performance benefits because i don't know how Java handles this.

Upvotes: 20

Views: 180463

Answers (4)

Tomasz Nurkiewicz
Tomasz Nurkiewicz

Reputation: 340883

Yes, Java (similar to other mainstream languages) uses lazy evaluation short-circuiting which means it evaluates as little as possible.

This means that the following code is completely safe:

if(p != null && p.getAge() > 10)

Also, a || b never evaluates b if a evaluates to true.

Upvotes: 45

Oleg Mikheev
Oleg Mikheev

Reputation: 17444

Please look up the difference between & and && in Java (the same applies to | and ||).

& and | are just logical operators, while && and || are conditional logical operators, which in your example means that

if(bool1 && bool2 && bool3) {

will skip bool2 and bool3 if bool1 is false, and

if(bool1 & bool2 & bool3) {

will evaluate all conditions regardless of their values.

For example, given:

boolean foo() {
    System.out.println("foo");
    return true;
}

if(foo() | foo()) will print foo twice, and if(foo() || foo()) - just once.

Upvotes: 12

Peter Lawrey
Peter Lawrey

Reputation: 533670

Is Java smart enough to skip checking bool2 and bool2 if bool1 was evaluated to false?

Its not a matter of being smart, its a requirement specified in the language. Otherwise you couldn't write expressions like.

if(s != null && s.length() > 0)

or

if(s == null || s.length() == 0)

BTW if you use & and | it will always evaluate both sides of the expression.

Upvotes: 17

Srinivas Reddy Thatiparthy
Srinivas Reddy Thatiparthy

Reputation: 11155

Yes,that is called short-circuiting.

Please take a look at this wikipedia page on short-circuiting

Upvotes: 6

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