Testing and Debugging

Debug Trace

A debug flag can print intermediate values while leaving the final result unchanged.

debug flag A flag lets diagnostic output be turned on or off without changing the calculation.
intermediate value Printing the intermediate values helps confirm how the result was built.

Debug Trace

debug
DebugTrace.java
Replay: real traced execution (multi-file project)
public class DebugTrace {
    public static void main(String[] args) {
        boolean debug = true;
        int width = 6;
        int height = 4;
        int area = width * height;

        if (debug) {
            System.out.println("debug width=" + width + " height=" + height);
        }

        System.out.println("area=" + area);
    }
}

public class DebugTrace {
    public static void main(String[] args) {
        boolean debug = false;
        int width = 6;
        int height = 4;
        int area = width * height;

        if (debug) {
            System.out.println("debug width=" + width + " height=" + height);
        }

        System.out.println("area=" + area);
    }
}

  1. debug ← true, width ← 6, height ← 4, area ← 24

    1public class DebugTrace {2    public static void main(String[] args) {3        boolean debug→ true = true;  //@debug=false, true4        int width→ 6 = 6;5        int height→ 4 = 4;6        int area→ 24 = width6 * height4;

  2. if (debug)

    8if (debugtrue) {9    System.out.println("debug width=" + width6 + " height=" + height4);10}
    outputdebug width=6 height=4

  3. System.out.println("area=" + area);

    12    System.out.println("area=" + area24);13}
    outputarea=24

  1. debug ← false, width ← 6, height ← 4, area ← 24

    1public class DebugTrace {2    public static void main(String[] args) {3        boolean debug→ false = false;4        int width→ 6 = 6;5        int height→ 4 = 4;6        int area→ 24 = width6 * height4;78        if (debug) {9            System.out.println("debug width=" + width + " height=" + height);10        }1112        System.out.println("area=" + area24);13    }
    outputarea=24