1. first search for the syntax errors

2. swith to debug mode and Search for for runtime errors and logic errors:

I will show you HOW TO USE THE TOOLS by using following example code:

package Debugging;

public class Project1 {	
	
	int add(int number1, int number2) {
		int answer = number1 - number2;
		return answer;
	}
	
	int minus(int number1, int number2) {
		int answer = number1 - number2;
		return answer;
	}
	
	void main () {
		int result = add(2,5);
		int answer = minus(result, 1);
		System.out.println(answer);
	}
	
	public static void main(String[] argv) {
		new Project1().main();
	}
	
}

OUTPUT: -4

If you calculate by hand: 2 + 5 – 1, this should be 6. However, the program gives the output -4.

To analyse where this goes wrong, use the debug tool:

Beforehand you should already have searched on syntax errors as described above.

1. Switch to “Debug Mode”
2. Create breakpoints; Mark the parts you want to analyse, by double clicking on the left side bar:
   

   A blue dot will appear (a blue dot is a breakpoint)

    

3. Press “Debug as”	Press or press directly the symbol if java already selected the right project

4. By using these tools, it is possible to go through the code:
   

   Key	Description
   F5	Executes selected line, whilegoing step-by-step into the line
   F6	Executes selected line, withoutgoing step-by-step into the line
   F7	Stepping out of the selected method
   F8	Resume program, until next breakpoint
   **	This is a “going back” tool. For example, useful when you want to go back in a method

   

5. This window “variables” shows the variables you have defined in the program
   After debugging line 6 of the method add, the answer is -3. This is already a weird result. Because add should give 2 + 5 = 7.
6. Therefore, look at the method add, which shows what the mistake was. In this case a logic error. The “-” sign is wrong, because it is an add function.
   int add(int number1, int number2) {
   	int answer = number1 - number2;
   	return answer;
   }

7. After changing the add-function the program gives the desired result.
   package Debugging;
   
   public class Project1 {
   	
   	int add(int number1, int number2) {
   		int answer = number1 + number2;
   		return answer;
   	}
   	
   	int minus(int number1, int number2) {
   		int answer = number1 - number2;
   		return answer;
   	}
   	
   	void main () {
   		int result = add(2,5);
   		int answer = minus(result, 1);
   		System.out.println(answer);
   	}
   	
   	public static void main(String[] argv) {
   		new Project1().main();
   	}
   
   }

   OUTPUT: 6