Simple if statement vs. normal if statement

Question

At Java byte code level, is there any difference between an simple if-statement (Example 1) and a normal if-statement (Example 2):

Example 1:

if (cond) statement;

Example 2:

if (cond) {
    statement;
}

The background of the question, is that I saw in "high performance" classes like java.awt.Rectangle and Point only the variant without curly braces.

Is there any speed benefit, or is that only code style?

Answer 1

Aparte from the maintainability of your code, in terms of performance is exactly the same. You will not gain speed up from removing {}, since {} it is not an instruction by it self.

I normal use with {} because makes the code easy to read (IMO) and less propitious to making errors.

This example:

public void A(int i) {
     if (i > 10) {
        System.out.println("i");
        }
    }

    public void B(int i) {
        if (i > 10)
            System.out.println("i");
    }

byte code generated:

 // Method descriptor #15 (I)V
  // Stack: 2, Locals: 2
  public void A(int i);
     0  iload_1 [i]
     1  bipush 10
     3  if_icmple 14
     6  getstatic java.lang.System.out : java.io.PrintStream [16]
     9  ldc <String "i"> [22]
    11  invokevirtual java.io.PrintStream.println(java.lang.String) : void [24]
    14  return
      Line numbers:
        [pc: 0, line: 5]
        [pc: 6, line: 6]
        [pc: 14, line: 8]
      Local variable table:
        [pc: 0, pc: 15] local: this index: 0 type: program.TestClass
        [pc: 0, pc: 15] local: i index: 1 type: int
      Stack map table: number of frames 1
        [pc: 14, same]

  // Method descriptor #15 (I)V
  // Stack: 2, Locals: 2
  public void B(int i);
     0  iload_1 [i]
     1  bipush 10
     3  if_icmple 14
     6  getstatic java.lang.System.out : java.io.PrintStream [16]
     9  ldc <String "i"> [22]
    11  invokevirtual java.io.PrintStream.println(java.lang.String) : void [24]
    14  return
      Line numbers:
        [pc: 0, line: 11]
        [pc: 6, line: 12]
        [pc: 14, line: 13]
      Local variable table:
        [pc: 0, pc: 15] local: this index: 0 type: program.TestClass
        [pc: 0, pc: 15] local: i index: 1 type: int
      Stack map table: number of frames 1
        [pc: 14, same]

As you can see the are the same.

Answer 2

The two are exactly the same. The Java compile will produce the same code.

Keep in mind, however, that in the non-bracket case, you will not be able to add multiple sub-statements inside the if-block the way you would be able to in the bracketed case

Answer 3

The two examples you gave do the same exact thing. Your first example is a simple if-then-statement, while your second example is a normal if-then statement.

The time it takes to execute those two statements is the same, since the braces are not an instruction, and therefore do not effect speed. I would still use the normal if statement though, so you can have as many statements as you want within the if-statement.