CODEWITHSUNDEEP
javacompiler-errors
Nitin
Nitin

Reputation: 83

Java compile time unreachable code error

I am getting compile time "unreachable code" error on below line in my program:

System.out.println("i =" + i + ", j = " + j);

public static void main(String[] args) {
    int i = 0, j = 5;
    tp: for (;;) 
    {
        i++;
        for (;;) 
        {
            if (i > --j) {
                break tp;
            }

        }
        System.out.println("i =" + i + ", j = " + j);
    }
}

kindly help me out to find the exact cause for this. Thanks in advance.

Upvotes: 2

Views: 222

Answers (3)

Tom
Tom

Reputation: 17597

The inner loop is an infinite loop. The only way to exit it is when i > --j is true, but this will break the outer loop (due to the call of break tp;) and the program will immediately execute the next code after the outer loop. That means there is no condition where the inner loop terminates "normally" so the next code after it can run.

Upvotes: 1

Luiggi Mendoza
Luiggi Mendoza

Reputation: 85799

Let's analyze this code:

tp: for (;;)  //<-- similar to while(true)
    {
        i++; //increases i by 1
        for (;;)  //<-- similar to while(true)
        {
            if (i > --j) { //decreases j and compares its value against i
                break tp; //breaks tp, which means breaking the outer for loop
            }
        }
        //while(true) above
        //if break gets executed, it breaks this for loop
        //so this line can never be executed
        System.out.println("i =" + i + ", j = " + j);
    }

Easiest solution:

Move System.out.println("i =" + i + ", j = " + j); outside the outer for loop.

tp: for (;;)
{
    i++;
    for (;;)
    {
        if (i > --j) {
            break tp;
        }
    }
}
System.out.println("i =" + i + ", j = " + j);

Upvotes: 7

rgettman
rgettman

Reputation: 178343

The System.out.println code can't be reached ever, even if i is greater than j. The only break sends you breaking out of the outer for loop. The System.out.println statement is after the inner for loop, but in the inner for loop, you either keep looping, decrementing j, or you break the outer loop. There is no way to reach the println statement.

To print what i and j are after the loop ends, move the System.out.println call after the ending brace of the outer for loop.

Upvotes: 3

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