原文地址:http://leihuang.org/2014/11/13/Cycular-Dependency/
假設我們有一個類A,它包含了一個B的對象,同時類B也包含了一個A對象。那麼此時不管你實例化哪一個類,都會出現StackOverflowError錯誤,這就是java對象循環依賴問題。類似於雞和蛋的問題。
首先我們看下面這段錯誤的代碼,分析其錯誤的地方。
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
這是上面代碼報的錯誤,因爲當你創建一個Chicken對象時,同時也需要一個Egg對象,而一個Egg對象也需要一個Chicken對象,這樣一直循環下去就發生了棧溢出的錯誤。
那麼如何來解決這個問題呢?我們可以給Chicken寫一個代理類ChickenProxy,這樣Egg包含的不再是Chicken而是代理類ChickenProxy,這樣就利用了第三方來解決循環依賴問題。代碼如下。
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 !