CODEWITHSUNDEEP
javaperformance
FirmView
FirmView

Reputation: 3150

What is the performance differences between if and logical operators

I was wondering would there be a performance differences while i use logical operators instead of several if statements. I saw a nice link, does this apply to java also?

Upvotes: 2

Views: 1526

Answers (3)

Pshemo
Pshemo

Reputation: 124275

I just created class like 

class Test{
    static java.util.Random r=new java.util.Random();
    boolean test(){
        return r.nextBoolean();
    }
    void test1(){
        if (test() && test() && test())
            System.out.println("3x yes");
    }
    void test2(){
        if (test())
            if (test()) 
                if (test())
                    System.out.println("3x yes");
    }
}

compiled it then decompiled by javap -c Test and got these result

class Test {
  static java.util.Random r;

  Test();
    Code:
       0: aload_0
       1: invokespecial #1                  // Method java/lang/Object."<init>":
()V
       4: return

  boolean test();
    Code:
       0: getstatic     #2                  // Field r:Ljava/util/Random;
       3: invokevirtual #3                  // Method java/util/Random.nextBoole
an:()Z
       6: ireturn

  void test1();
    Code:
       0: aload_0
       1: invokevirtual #4                  // Method test:()Z
       4: ifeq          29
       7: aload_0
       8: invokevirtual #4                  // Method test:()Z
      11: ifeq          29
      14: aload_0
      15: invokevirtual #4                  // Method test:()Z
      18: ifeq          29
      21: getstatic     #5                  // Field java/lang/System.out:Ljava/
io/PrintStream;
      24: ldc           #6                  // String 3x yes
      26: invokevirtual #7                  // Method java/io/PrintStream.printl
n:(Ljava/lang/String;)V
      29: return

  void test2();
    Code:
       0: aload_0
       1: invokevirtual #4                  // Method test:()Z
       4: ifeq          29
       7: aload_0
       8: invokevirtual #4                  // Method test:()Z
      11: ifeq          29
      14: aload_0
      15: invokevirtual #4                  // Method test:()Z
      18: ifeq          29
      21: getstatic     #5                  // Field java/lang/System.out:Ljava/
io/PrintStream;
      24: ldc           #6                  // String 3x yes
      26: invokevirtual #7                  // Method java/io/PrintStream.printl
n:(Ljava/lang/String;)V
      29: return

  static {};
    Code:
       0: new           #8                  // class java/util/Random
       3: dup
       4: invokespecial #9                  // Method java/util/Random."<init>":
()V
       7: putstatic     #2                  // Field r:Ljava/util/Random;
      10: return
}

As you can see bytecodes of test1 and test2 are same, so there is no difference in using 

    if (test() && test() && test())

or 

    if (test())
        if (test()) 
            if (test())

Upvotes: 4

user207421
user207421

Reputation: 311054

Both forms compile to the same code. Contrary to the suggestions in other answers, this is not an 'optimization', and it would be astonishing if different compilers did different things. There is only one sensible way to compile && and that is by treating it the same as another 'if'. I can't even think of a non-sensible way.

Upvotes: 0

mikera
mikera

Reputation: 106401

It's implementation dependent - so you'll need to benchmark to be sure.

Having said that, most JIT compilers are smart enough to optimise boolean comparisons very effectively so you are unlikely to see any difference.

The only area where logical operators are likely to offer a substantial advantage are in cases where you are using them to perform bitwise computations. This can be very efficient since it can result in branchless code that exploits hardware instructions.

Upvotes: 0

Related Questions