What does this line mean in Java: boolean retry = id == 1;

I have been learning Java for a while now and still learning new syntax tricks and stuff. I came across this in Android source code:

boolean retry = id == 1;

What does it mean?

id == 1 is a boolean expression which is true if id equals 1, and false otherwise.

boolean retry = id == 1; declares a boolean variable named retry, and assigns the value of the boolean expression id == 1 to this variable.

So it declares a boolean variable which is true if id == 1, and false otherwise.

To make it a bit clearer, you might write it that way:

boolean retry = (id == 1);

retry is true if id has the value 1, otherwise retry is false.

It is the same as

boolean retry;
if (id == 1)
   retry = true;
else
   retry = false;

==, which is the equality predicate, has a higher precedence than =, which is the assignment operator.

Therefore, id == 1 is evaluated first and then its value (either true or false) is assigned to retry.

The boolean retry gets the value of true if id == 1.

It's the same as:

boolean retry;
if (id == 1) {
    retry = true;
} else {
    retry = false;
}

first the id is evaluated with 1, so presumably id is an integer.

After that, the value retry is assigned this evaluation, so if id is equal to 1, retry will become true, and for any other value of id retry will become false.

This line creates a boolean variable and sets it to true if id is equal to 1 and false if it is not.

It is acts like a ternary operation, (x) ? true : false in C, C++, C#, etc;

The similar syntax:

boolean retry = (id == 1)? true: false; 

Or it can written another way:

boolean retry;
if (id == 1) {
    retry = true;
} else {
    retry = false;
}

I find that just using parens helps to clear up the confusion behind complex statements like this.

boolean retry = (id == 1); Makes much more sense to me. Here it's clear that (id == 1) is an expression being evaluated and the result is being assigned to boolean retry

It is a way of defining a boolean variable.

When id is 1, the value of retry will be true.

retry assigns an expression which will be either true or false as retry is a boolean. Further, == will be solved first and then it will be assigned to retry.

It might be easier to see whats happening if you look at it like this:

boolean retry = (id == 1);

So basically it checks if id equals 1, and then assigns the result to the variable retry.

It is basically the same as retry = (id == 1). It is evaluating the boolean expression, and assigning it to retry.

The Boolean variable retry will get value 0 or 1 depending on whether the expression id==1 returns true or false.

If value of id is 1, then id==1 will correspond to true, thus retry=1.

And if value of id is 0, then id==1 will correspond to false, thus retry=0.

Please note that == is a comparison operator.

I will base my response on the assumption that id is an int hence the comparison against 1 is proper and a compilation error is not in place. == is the equality operator in java as described in section 15.21.1 of the JLS. Being a boolean operator, == will output a boolean value. = is the java's assignment operator, in this particular case it's the compound assignment operator having the following syntax: > boolean f = (op1 op op2)

In translation = assigns the output value of the (op1 op op2) operation to the left operand, in this case f.

Looking back to your sample, the output of id == 1 (true if id has the value 1, false otherwise) is assigned to retry.

To conclude in plain english, your sample has the following meaning: Retry as long as id has the value 1.

1.int id = 1;
  boolean retry = id == 1;
    

which means retry = true;.

2.int id = 2;
  boolean retry = id == 1;
    

which means retry = false;.

Simplification id == 1 can be consider as

if ( id == 1 ){
}

The code can write just like this,then it will be understood easily,do you think so? Last, thanks you for giving the chance to answer the question!

boolean retry = (id == 1);