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vmware虚拟机下ubuntu扩大磁盘容量

西特张 03-26 06:00 阅读 2
父类写无参构造,子类不写构造,实例化子类,会同时调用父类构造方法
public class Father {

    private String name;
    private int age;

    public Father() {
        System.out.println("父类无参构造");
    }

}
public class Son extends Father {
    private String name;
    private int age;
}
public static void main(String[] args) {
        Son son = new Son();
 }

父类写无参构造,子类无参构造,实例化子类,会先调用父类构造方法,再调用子类构造
public class Father {

    private String name;
    private int age;

    public Father() {
        System.out.println("父类无参构造");
    }

}
public class Son extends Father {
    private String name;
    private int age;

    public Son() {
        System.out.println("子类无参构造");
    }
}
public static void main(String[] args) {
        Son son = new Son();
 }

父类没有无参构造,子类必须明确指定调用父类的哪个构造函数,并在子类的构造函数中使用 super 关键字调用。并且super必须在构造函数第一行,否则编译报错
public class Father {

    private String name;
    private int age;

    public Father(String name, int age) {
        this.name = name;
        this.age = age;
        System.out.println("父类有参构造");
    }

}

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