Is it possible to freeze System.currentTimeMillis() for testing

Question

For some testing purposes I would like to predict exactly what System.currentTimeMillis() will return. Is there any way in which I can freeze or manually set what w

Answer 1

Yes, solution exists:

For testing purposes you may create your own wrapper System, for example

package my.pack;

import java.io.PrintStream;

public class System
{
    // reuse standard System.out:
    public static PrintStream out = java.lang.System.out;

    // do anything with chosen method
    public static long currentTimeMillis()
    {
        return 1234567;
    }

}

and import it into your class which you want to test

import my.pack.System;

In that case all calls to System will be passed through your own System class.

NOTE:

• This is a solution for "how to intercept System.currentTimeMillis()"

• This is NOT suitable for automatic testing

• This is NOT an example of "how-to-design-a-good-program". If you ask for a good design, then you need to refactor your code, replace System.currentTimeMillis() - see other answers.