MrKamal Joshi

Seetharaman Venkatasamy wrote:
It is an expected output! constructor calls itself again since you are calling the constructor from instance filed declaration(initialization block)

This means in a class anything outside the method will be implicitly under a initialization block.

I was experimenting with inner class and got some problems
//Learning concepts of inner class class Outer { String Name; Outer(String x){this.Name=x;} public String toString(){return Name;} InnerNonStatic i1=new InnerNonStatic("First");//non static context of outer class therefore inner class object can be directly created //Outer.InnerNonStatic i3=new Outer("Second").new InnerNonStatic("Third");//causing problem void printa() { S.op(this+" of class "+this.getClass().getName()+" invokes the method of Outer class"); InnerNonStatic i2=new InnerNonStatic("Second");//you can create the object of inner class directly in outer class if the context is non static i2.print(); } public static void main(String[]args)//static context of outer class begins { Outer o1=new Outer("First Object"); o1.printa();// you can't access inner class members directly..you have to create the instance of inner to do this Outer.InnerNonStatic i3=o1.new InnerNonStatic("Third");//note o1 can also be replaced by new Outer() i3.print(); } class InnerNonStatic { String Name; InnerNonStatic(String x){this.Name=x;} public String toString(){return Name;} //InnerNonStatic i4=new InnerNonStatic("Fourth");//causing problem void print() { S.op(this+" Object of class "+this.getClass().getName()+" invokes the method of inner class"); } } }
Q1)Line 24.Why we have to redeclare Name inside inner as it was already been declared in outer class and members of outer class are also members of inner class?
Q2)Line 8 or 27 after omitting // and running the program i came across a weird output like that of infinite loop.What's that?

Actually you are making a mistake in printing out the elements of the array loc.You have written System.out.println(loc[cell]); where cell refers to values in array loc,and cell can have value greater than 2 which is outside the bounds of array loc.You have to use System.out.println(cell); for printing out array loc elements.

I tried to populate array by using for each loop but it's not working
import java.util.*; class Prg4 { static int[] a=new int[5]; public static void main(String[]ags) { for(int b:a) { Random r=new Random(); b=r.nextInt(20);//will generate random number between 0 and 20 } for(int b : a) { S.op(b); } } } class S { static<T>void op(T t) { System.out.println(t); } }

Yeah got it.I was making silly mistake.Thanks

import java.util.*; class MyList { List l1; List<String> l2; //We create two list one simple list and one generic list MyList(String s) { if(s=="Simple") { l1=new ArrayList(); } else { l2=new ArrayList<String>(); } } } class Prg3 { public static void main(String...arg) { System.out.println("Hello"); MyList li=new MyList("Simple"); MyList lii=new MyList("Generic"); //Adding elements in both the list li.l1.add("kamal"); lii.l1.add("kamal"); //Retriving elements from both the list System.out.println((String)li.l1.get(0)); System.out.println(lii.l1.get(0)); } }
Why i am getting NullPointerException here?

Thanks

Matthew Brown wrote:Why do you have a <T> at the front of your constructor? Try deleting that, and I suspect it will work.

What I think is happening here is that the <T> there is being used to define a generic method. This is separate from the T defining the generic class. So you've actually got two different Ts meaning different things, which leads to a conflict. On line 6 you're trying to assign from one to the other.

So it means that if i have a Generic class class Element<T,S> and i declare 3 constructors <T>Element(){}<S>Element(int a,int b){}<T,S>Element(int a,int b,int c){} then all <T> will be different?
class Element<T,S> { <T>Element(){}<S>Element(int a,int b){}<T,S>Element(int a,int b,int c){} }

Yeah,It works when i remove <T> in front of the constructor.Thanks

class Element<T> { T t; <T>Element(T t) { this.t=t; } T returnType() { return t; } } class Prg1 { public static void main(String...arg) { Element<Integer> obj2=new Element<Integer>(100); System.out.println(obj2.returnType()); } }
Compiling results in an error
incompatible types
found : T
required: T
this.t=t;
^
Please Explain

Thanks all.

Personally i use Textpad<www.textpad.com/download/>.It provides facility to write,compile and run the code.

You have to declare main as static.main is the entry point of a class. In java everything thing is written in a class.Now when you run java filename on command prompt, loader will load the class and jvm will search the main method to enter into the class. so making the main() as static, will make jvm access it directly through classname.main()

import java.util.regex.*; class Regexx { public static void main(String...NaN) { int i=0; Pattern p=Pattern.compile("\\d"); Matcher m=p.matcher("ab9sd9 9 ab n,a9b999ab");// p=p.compile("\\s"); while(m.find()==true)i++;System.out.println("No of spaces= "+i); } }
Above code generates output according to previous pattern("\\d") why so?

How the instance of an abstract class is created?As there exist a getInstance() method for an abstract class java.util.Calender.