无法理解Java中的流控制

Question

I am able to solve the attached code from a coding website.However,My answer is different from the website's answer.Below posted is the code.

static boolean b1, b2;
public static void main(String [] args) 
{
    int x = 0;
    if ( !b1 ) /* Line 7 */
    {
        if ( !b2 ) /* Line 9 */
        {
            b1 = true;
            x++;
            if ( 5 > 6 ) 
            {
                x++;
            }
            if ( !b1 ) 
                x = x + 10;
            else if ( b2 = true ) /* Line 19 */
                x = x + 100;
            else if ( b1 | b2 ) /* Line 21 */
                x = x + 1000;
        }
    }
    System.out.println(x);
}
}

My idea:

Initially,b1=false and b2= false,it passes the first two if conditions and sets b1 to true besides incrementing the value of x to >1. From there on it starts failing for every condition and prints the >final value to be 1.

Website's Solution:

As instance variables, b1 and b2 are initialized to false. The if tests
on lines 7 and 9 are successful so b1 is set to true and x is
incremented. The next if test to succeed is on line 19 (note >that the
code is not testing to see if b2 is true, it is setting b2 to be >true).
Since line 19 was successful, subsequent else-if's (line 21) >will be
skipped.The final value of x is 101

What I do not understand from the website solution:

"note that the code is not testing to see if b2 is true, it is setting b2 to be true". How can it set the value of b2 to "true" without testing it's status?

Any Suggestions can be highly helpful!

Answer 1

Line 19 is:

else if ( b2 = true )

The coding website is probably trying to teach you about a common programming mistake, ie. using assignment = instead of comparison == .

The code (as written above) is assigning the value of true to b2 rather than comparing the value of b2 to true . The result of the assignment expression is true hence the if will always succeed and its code block will be executed. This will happen regardless of the value of b2 prior to executing this line of code.

If you use what was probably intended, ie:

else if ( b2 == true )

then a comparison will take place and the if expression (and the execution of its block) will depend on the value of b2 .