1.Constructor running order of Base class and Derived class
This is Alibaba's audition problem.
class A{
A(int x){
System.out.println(x);
}
}
class B{
A m=new A(1);
B(){
m=new A(2);
}
}
class C extends B{
A n=new A(3);
C(){
n=new A(4);
}
}
public class ali {
public static void main(String[]args){
new C();
}
}
output :
1
2
3
4
java Is different from C#.
java:Base class first
Base class member define.
Base class constructor
Derived class member define.
Derived class constructor.
C#:member define first
Base class member define.
Derived class member define.
Base class constructor.
Derived class constructor.
2.Derived class constructor will call Base class constructor.
//子类的构造函数会调用父类构造函数
class one {
public one(){
System.out.println("one");
}
}
class two extends one{
public two (){
System.out.println("two");
}
public two(String s){
System.out.println("two "+s);
}
}
class three extends two{
public three(){
this("haha");
System.out.println("three");
}
public three(String s){
super("haha");
System.out.println("three "+s);
}
}
public class Construct {
public static void main(String[]args){
new three();
}
}
3.i++
4.
5.
6.接口继承
interface A{
int n=3;
void fun();
}
interface B{
int n=3;//都是final类型的默认。
void fun();
}
class C implements A,B{
public C(){
//n=4;//wrong ,ambiguous二义性
//A.n=4;//wrong,final 类型不可赋值
}
public void fun(){//函数不会有二义性,只要有这个函数，就算实现了借口
}
}
public class InterfaceTest {
public static void main(String[]args){
new C().fun();
}
}