Change the Random.java class

You will need these Handy bash scripts before you do any of the below.

$ cd $HOME/sources/jdk8/

or

$ cd $HOME/sources/jdk8_tl/

or

$ cd $HOME/sources/jdk9/

$ gedit jdk/src/share/classes/java/util/Random.java

or

$ gedit jdk/src/java.base/share/classes/java/util/Random.java

Locate the next() function in Random.java

protected int next(int bits) {
    return 100;                     ⇐   our code

     /*long oldseed, nextseed;    ⇐    commented block
     AtomicLong seed = this.seed;
     do {
         oldseed = seed.get();
         nextseed = (oldseed * multiplier + addend) & mask;
     } while (!seed.compareAndSet(oldseed, nextseed));
     return (int)(nextseed >>> (48 - bits));*/
}

$ gedit ChangeRandom.java 

import java.util.Random;

public class ChangeRandom {
    public static void main(String[] args) {
        System.out.println();
        Random someRandom = new Random();
        int letSeeWhatIGet = someRandom.nextInt();
        System.out.println(letSeeWhatIGet);
        int letSeeWhatIGetAgain = someRandom.nextInt();
        System.out.println(letSeeWhatIGetAgain);

        if (letSeeWhatIGet == letSeeWhatIGetAgain) {
           System.out.println("Its printing the same number over-and-over again! That's not random.");
        } else {
           System.out.println("Its printing a different number each time! Now that is random.");
        }
    }
}

$ make images
.
.
.
$ bash buildAndRunTheChangedRandom.sh

Output
100
100
Its printing the same number over-and-over again! That's not random.

Note: nextInt() calls next() with a parameter which is ignored and instead returns the hardcoded 100.

Undo your changes to jdk/src/java.base/share/classes/java/util/Random.java or jdk/src/share/classes/java/util/Random.java and rebuild the images by running.

To undo the changes, one can use:

$ cd jdk/src/share/classes/java/util

or

$ cd jdk/src/java.base/share/classes/java/util

$ hg revert Random.java

$ make images