package pkg;
class Str23{//1st class
String s;// you will see in output that String s is point to NULL
Str23(String st){// self-defined constructor
s=st;
System.out.println("Created,i am: "+s);
}
Str23(){//default constructor
System.out.println("Created,i am: "+s);
//nothing,i want to know what it is contained in s by deafault
}
}
class Rock2{//2nd class
Rock2(int i){// the constructor with a input
System.out.println("Rock: "+i);
}
}
public class p77 {
public static void main(String[] args){
Object Rock2;
Object Str23;
for (int i=0;i<10;i++)
new Rock2(i);
System.out.println("Now,go to see what contained in Str23");
Str23 st=new Str23();// this can discover what it is in String when it is initialized
System.out.println(st);
Str23 sp=new Str23("Maomao");
System.out.println(sp);
}
}
OUTPUR:
Rock: 0
Rock: 1
Rock: 2
Rock: 3
Rock: 4
Rock: 5
Rock: 6
Rock: 7
Rock: 8
Rock: 9
Now,go to see what contained in Str23
Created,i am: null
pkg.Str23@15db9742
Created,i am: Maomao
pkg.Str23@6d06d69c