super() 有什么用?

super() 是调用父类的构造函数啦,如果在代码中无super()的话,还会不会调用父类的构造函数?

 

class Person { public static void prt(String s) { System.out.println(s); } Person() { prt("A Person."); } Person(String name) { prt("A person name is:" + name); } }

public class Chinese extends Person { Chinese() { super(); // 调用父类构造函数（1） prt("A chinese.");// (4) } Chinese(String name) { super(name);// 调用父类具有相同形参的构造函数（2） prt("his name is:" + name); } Chinese(String name, int age) { this(name);// 调用当前具有相同形参的构造函数（3） prt("his age is:" + age); } public static void main(String[] args) { Chinese cn = new Chinese(); cn = new Chinese("kevin"); cn = new Chinese("kevin", 22); } }

结果:

A Person. A chinese. A person name is:kevin his name is:kevin A person name is:kevin his name is:kevin his age is:22

可见,子类在构造自己时会调用父类相关的构造函数的

super()就调用父类无参的构造函数

super(name)   父类1参数构造函数

this(name)   自己的1参数构造函数

 

如果不写super会如何?

public class Chinese extends Person { Chinese() { //super(); // 调用父类构造函数（1） prt("A chinese.");// (4) } Chinese(String name) { //super(name);// 调用父类具有相同形参的构造函数（2） prt("his name is:" + name); } Chinese(String name, int age) { //this(name);// 调用当前具有相同形参的构造函数（3） prt("his age is:" + age); } public static void main(String[] args) { Chinese cn = new Chinese(); cn = new Chinese("kevin"); cn = new Chinese("kevin", 22); } }

结果

A Person. A chinese. A Person. his name is:kevin A Person. his age is:22

可以看到子类还是会调用父类的构造函数,是无参数的那个构造函数