if(x) 和 if(x==true) 一样吗？

Question

Ok, so let's say I have an if statement and a boolean x:

if (x) {
    // some stuff
}

What happens here? Does this mean the same thing as if(x == true) ?

Answer 1

Yes,

if(x) {

}

is the succinct equivalent of

if(x == true) {

}

As @Sotirios points out, they are different at the bytecode level. Consider the following Java class:

class Test { 
   public void foo() { 
      boolean x = true;
      if(x == true) { 
      }
   }
}

emits:

  public void foo();
    Code:
       0: iconst_1      
       1: istore_1      
       2: iload_1       
       3: iconst_1      
       4: if_icmpne     7
       7: return 

vs

class Test { 
   public void foo() { 
      boolean x = true;
      if(x) { 
      }
   }
}

which emits:

  public void foo();
    Code:
       0: iconst_1      
       1: istore_1      
       2: iload_1       
       3: ifeq          6
       6: return  

I don't think this has any bearing on the performance or correctness of the program.

Answer 2

Yes, it is.

if checks if the condition is true, and if it is, executes the body statement. So x needs to be a boolean expression.

In fact x is equivalent to x == true if x is a boolean expression, so you should use x as it is more concise. This becomes clearer if the variable has a proper name for a boolean, eg

if (this.isVisible()) {
    this.hide();
}

vs.

if (this.isVisible() == true) {
    this.hide();
}

The first one is better to read.

Answer 3

是的，这与 if(x == true) 的含义相同。

Answer 4

如果x可以解析为布尔值，并且值为“true”，则将执行“其他内容”。

Answer 5

Yes, it is same as if(x == true) . In fact if(x) is recommended.

See the examples in The if-then and if-then-else Statements in The Java tutorial.

Answer 6

The return of both is a boolean, in this case both return true

For example:

x= true.

Evaluating:

a) if(x)

b) if(x==true)

Both return true, the first because is the value directly and the second because the expression it is true (true==true).

Hope this can help you too...

http://www.homeandlearn.co.uk/java/boolean_values.html

Answer 7

Jep this is right.

There is also a short form that could be interesting for you:

It means if x is true then return true, else return false.

(x) ? return true : return false;

Answer 8

Short answer: yes.

An if statement takes a boolean expression as its condition. That can be the result of an operator which returns a boolean value such as == , or that can be a boolean variable. Basically, a boolean expression is anything which you can assign to a boolean variable:

boolean b = ?;

Therefore, x == true is somewhat redundant, as x on its own already suffices: those two boolean expressions are equivalent . It's quite common for new programmers though to write the == true , as it "reads" more naturally: if x is true, then do...

However, you should actually read that as if (x == true) is true, then do... as that's what's actually happening. Here, you see where the redundancy comes from. More experienced programmers know this and prefer writing x and !x as opposed to x == true and x == false respectively. It doesn't matter for the compiler, but it matters for the programmer/maintainer when he has to read:

if ( ((x == true) && (y == true)) || (z == false) ) { ... }

as opposed to:

if ( (x && y) || !z ) { ... }

Answer 9

Does this mean the same thing as if(x == true) ?

Yes if(x == true) will give same results as if (x) . It is based on simple logic:

• if x is true condition x == true is same as true == true which is evaluated to true which is same as original value of x
• if x is false condition x == true is same as false == true which is evaluated to false which again is same as original value of x

So regardless of value of x expression if (x==true) is equivalent to if (x) .

Answer 10

Yes, both are Same & True . And give you the same result.

if(x) is more appropriate

Reason, In Programming language, any number but not 0 is considered as True .

Suppose I take a number which is 5 :

if(x) or if(5)

because 5 is not equal to 0 or you can say 5!=0 that why it's True.