Share the world: 2012

如果你認為自己係Java高手，恭喜你， show time !!!

RULES：
1). 唔準runtime改code, 改class, 改memory, 即係無得用我最愛的setAccessible()
2). 除左(1) 同題目既要求之外，你點寫都得，總之要做到
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Introduction

This is the first in a series of Java puzzles, that put your Java skills to the test, in a challenging and fun way!
A puzzle consists of some given Java code with a line in it that seems to be impossible to reach. It’s up to you to find the hole in it, abuse a subtle behavior of Java to make execution reach that line anyways.

There almost aren’t any rules; any cheating inside your code is allowed; it is the whole point of the puzzle. [Clarification: Cheating the environment is not]. You must run with the security manager enabled (java -Djava.security.manager), otherwise it would be too easy (with setAccessible for example). [Update: Use common sense, and see the exact rules if you're in doubt].

The puzzle

How can you fit 20 clowns into a Volkswagen? Two classes are given: an empty Clown class, and a Volkswagen class to which you can add clowns. When you try to add a Clown, it is checked that it isn’t already full. But if you just try hard enough, there’s always room for some extra clowns…

package clowns;

public class Clown {

}

package clowns;

import java.util.HashSet;

import java.util.Set;

public class Volkswagen {

    private static final int CAPACITY = 5;

    private Set<Clown> clowns = new HashSet<Clown>();

    public synchronized void add(Clown clown) {

        if (clowns.size() >= CAPACITY) {

            throw new IllegalStateException("I'm full");

        } else {

            clowns.add(clown);

        }

    }

    public synchronized void done() {

        if (clowns.size() == 20) {

            // The goal is to reach this line

            System.out.println("I'm a Volkswagen with 20 clowns!");

        }

    }

}

Write a class that when executed pushes 20 clowns into the little car, and reaches the marked line. Here is one that won’t really work, just to get you started:

package you;

import clowns.Clown;

import clowns.Volkswagen;

public class You {

    public static void main(String args[]) {

        // TODO put 20 clowns into a Volkswagen

        Volkswagen vw = new Volkswagen();

        for (int i = 0; i < 20; i++) {

            vw.add(new Clown());

        }

        vw.done();

    }

}

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PS: 這不是我出的題目，出題目既堅係神人
PSS: 真係好tricky
PSSS: 佢既下一條都好屈機

refs: http://wouter.coekaerts.be/2012/puzzle-clowns

Share the world

Sunday, February 26, 2012

Life is wonderful

Java Puzzle

Introduction

The puzzle