Java object dependency

Java object dependency

Address: http://leihuang.org/2014/11/13/Cycular-Dependency/

Suppose we have A class A, which contains an object of B, and Class B also contains an object of. At this time, StackOverflowError will occur no matter which class you instantiate. This is a java object loop dependency problem. Similar to chicken and egg problems.

First, let's take a look at the following error code and analyze the error.

public class CyclicDependencies {    public static void main(String args[]){        Chicken c = new Chicken() ;        //Egg e = new Egg() ;    }}class Chicken{    private Egg e ;    private int age ;    public Chicken(){        e = new Egg() ;        setAge(10) ;    }    public int getAge() {        return age;    }    public void setAge(int age) {        this.age = age;    }}class Egg{    private Chicken chicken ;    private int weight ;    public Egg(){        chicken = new Chicken() ;        setWeight(1) ;    }    public int getWeight() {        return weight;    }    public void setWeight(int weight) {        this.weight = weight;    }}

Exception in thread "main" java.lang.StackOverflowError

This is an error reported by the code above, because when you create a Chicken object, you also need an Egg object, and an Egg object also needs a Chicken object, in this way, the stack overflow error occurs during the loop.

So how can we solve this problem? We can write a ChickenProxy proxy for the Chicken, so that Egg does not include Chicken but the ChickenProxy of the proxy class, so that a third party is used to solve the circular dependency problem. The Code is as follows.

public class CyclicDependencies {    public static void main(String args[]){        Chicken c = new Chicken() ;        Egg e = new Egg(c) ;        System.out.println(c.getAge());        System.out.println(e.getWeight());    }}interface ChickenProxy{    int getAge();    void setAge(int age) ;}class Chicken implements ChickenProxy{    private Egg e ;    private int age ;    public Chicken(){        e = new Egg(this) ;        setAge(10) ;    }    public int getAge() {        return age;    }    public void setAge(int age) {        this.age = age;    }}class Egg{    private ChickenProxy chicken ;    private int weight ;    public Egg(Chicken c){        chicken = c ;        setWeight(1) ;    }    public int getWeight() {        return weight;    }    public void setWeight(int weight) {        this.weight = weight;    }}

15:41:41

Brave, Happy, Thanksgiving!