协变类型返回也是覆盖方法的一种，jdk5开始支持的一种:子类覆盖方法返回可以是子类返回的子类,这个比较拗口
/*
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* and open the template in the editor.
*/
package com.fengli;
/**
* 粮食类
* @author Administrator
*/
public class Grain {
public String toString(){
return "Grain";
}
}
/*
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*/
package com.fengli;
/**
* 小麦类
* @author Administrator
*/
public class Wheat extends Grain{
@Override
public String toString(){
return "Wheat";
}
}
/*
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* and open the template in the editor.
*/
package com.fengli;
/**
*协变返回
* 子类覆盖方法返回可以是子类返回的子类,这个比较拗口
* @author Administrator
*/
public class CovariantReturnType {
class Mill {
public Grain process() {
return new Grain();
}
}
class WheatMill extends Mill {
@Override
public Wheat process() {
return new Wheat();
}
}
public static void main(String[] args) {
CovariantReturnType c = new CovariantReturnType();
CovariantReturnType.Mill m = c.new Mill();
Grain g = m.process();
System.out.println(g.toString());
CovariantReturnType.Mill wm = c.new WheatMill();
Grain g1 = wm.process();
System.out.println(g1.toString());
}
}