How do I make all my main methods show execution time

Question

It has been a while since I've programmed in Java and I just can't seem to solve it so I apologize in advance for anything stupid I might have done.

I am currently solving a list of math problems in Java. I create a new class called ProblemX for every problem. I want each class to print the duration time of the execution. Rather than programming this in each seperate class I though I'd use some inheritance but that's where I got stuck.

Public abstract class Problem{

 public static void main(String[]args){
   Problem p = new Problem();
   long startTime = System.nanoTime();
   p.solve();
   long endTime = System.nanoTime();
   System.out.println("Execution time: " + (endTime - startTime) + " nanoseconds");
 }

abstract void solve();

}

This doesn't work because I can't create an instance of Problem in an abstract class. I can't use a Solveable interface because then Problem has to define 'solve'.

Obviously I'm missing something here so if anyone could help it would be greatly appreciated.

Answer 1

How about:

public abstract void solve();

public void solveProblem() {
    startTime();
    solve();
    endTime();
    System.out.println(timeTaken);
}

Then just override solve and call solveProblem.

Answer 2

You can do something like

public abstract class Problem{

    long startTime;

    long endTime;

    public void startTime(){
    startTime = System.nanoTime();
    }

    public void endTime(){
    endTime = System.nanoTime();
    }

    public long measure(){
    return endTime - startTime;
    }

}

public class ProblemX extends Problem{

    public static void main(String[] a){
     ProblemX x = new ProblemX(); 
     x.startTime();
     //do your work
     x.endTime();
     System.out.println("time taken" + x.measure());
    }
}

Answer 3

Something like this perhaps?

package com.stackoverflow;
public abstract class Problem {
    public static void main(String[] args) {
        Problem p = new Problem(){

            @java.lang.Override
            protected void doCalculation() {
                for (int i = 0; i < 1000; i++) {
                    System.out.println("Printing number... " + i);
                }
            }
        };
        p.solve();
        System.out.println("Execution time: " + p.getElapsedTime() + " nanoseconds");
    }

    private long startTime, endTime;
    private void doStartTime() {
        startTime = getSystemNanoTime();
    }
    private void doEndTime() {
        endTime = getSystemNanoTime();
    }
    private long getSystemNanoTime() {
        return System.nanoTime();
    }
    protected abstract void doCalculation();

    public void solve() {
        doStartTime();
        doCalculation();
        doEndTime();
    }
    public long getElapsedTime() {
        return endTime - startTime;
    }

}

lets say that you have a ProblemX class which overrides Problem. you should change the following rows in the static main method:

from:

Problem p = new Problem(){

@java.lang.Override
protected void doCalculation() {
    for (int i = 0; i < 1000; i++) {
        System.out.println("Printing number... " + i);
    }
}

};

to:

Problem p = new XProblem();