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java对象循环依赖问题


假设我们有一个类A,它包含了一个B的对象,同时类B也包含了一个A对象。那么此时不管你实例化哪一个类,都会出现StackOverflowError错误,这就是java对象循环依赖问题。类似于鸡和蛋的问题。

首先我们看下面这段错误的代码,分析其错误的地方。

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

这是上面代码报的错误,因为当你创建一个Chicken对象时,同时也需要一个Egg对象,而一个Egg对象也需要一个Chicken对象,这样一直循环下去就发生了栈溢出的错误。

那么如何来解决这个问题呢?我们可以给Chicken写一个代理类ChickenProxy,这样Egg包含的不再是Chicken而是代理类ChickenProxy,这样就利用了第三方来解决循环依赖问题。代码如下。

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;
    }
}

2014-11-13 15:41:41

Brave,Happy,Thanksgiving !


java对象循环依赖问题