向上轉型:子類轉父類

Father father1= new Son();

向下轉型:父類轉子類

Son son = (Son)new Father (); // 這樣是運行時會報錯

Father father1 = new Son(); Son son1 = (Son) father1; // 這樣不報錯

通過寫一個方法把父類轉換為子類

class Father {

    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        
 
this.name = name;
    }

    /**
     * 將當前對象轉換為子類對象
     *
     * @param clazz 目標類型
     * @return 目標對象
     */
    public <T extends Father> T to(Class<T> clazz) {
        T instance;
        try {
            instance = clazz.newInstance();
        } catch (Exception e) {
            throw
 
 new IllegalArgumentException("Failed to create " + clazz.getSimpleName() + " instance.", e);
        }

        instance.setName(this.getName());
        return instance;
    }
}

public class Son extends Father {

    private String age;

    public String getAge() {
        return age;
    }

    
 
public void setAge(String age) {
        this.age = age;
    }

    public static void main(String[] args) {

        // 子類轉父類,父類再轉子類
        // Father father = new Son();
        // Son son = (Son) father;

        // 父類直接轉子類
        // Son son =  (Son)new Father (); // 運行時會報錯

        // 父類通過方法轉直接轉子類
        Father father = new Father();
        Son son = father.to(Son.class);
    }

}

java 向上轉型與向下轉型