继承时的入参和出参

入参：父子和子类的入参类型需要保持一致

出参： 子类的出参可以与父类相同，也可以是父类的子类

public class MapParent {
    public Map testMap(Map param) {
        System.out.println("bbb" + param);
        return (HashMap)param;
        
    }
}


public class MapSub extends MapParent {
    
    @Override
    public HashMap testMap(Map param) {
        System.out.println("ddd" + param);
        return (HashMap) param;
        
    }
}


public class TestMap {

    public static void main(String[] args) {
        MapParent mapParent = new MapParent();
        Map param = new HashMap<>();
        Map result = mapParent.testMap(param);
        System.out.println("aaa" + result);

        mapParent = new MapSub();
        result = mapParent.testMap(param);

        System.out.println("aaa" + result);
    }

}