class X : value and child
==========================
/*
class H {	
	public String toString() { return "cs2312";} 
}

public class Main{
   public static void main(String[] args) {
	   H obj = null;	
	   System.out.println(obj);
   }
}
*/

class X {
	private int xValue;
	private X xChild;

	public X(int xValue, X xChild) {
		this.xValue = xValue;
		this.xChild = xChild;
	}

	public String toString() {

		return xChild + " " + xValue;
	}
}

public class Main {
	public static void main(String[] args) {

		// X obj = null;
		X obj = new X(99, new X(88, new X(77, null)));

		System.out.println(obj);
	}
}



class X: doSomething()- sees 3 objects
====================================== 
class X {
	private	int data;
	public X(int d) {data=d*2;}
	public String toString() {return ""+data;} //a trick to make a string quickly
	
	public void doSomething(X r)	{

		X s = new X(8);

		System.out.println(this.data);
		System.out.println(r.data);
		System.out.println(s.data);
	}
}

public class Main {

   public static void main(String[] args) {

	   X a = new X(1);
	   X b = new X(15);
	   a.doSomething(b);
   }
}


setName()
=====================
class Employee {
	private String id, name;
	public Employee(String aId, String aName) { id= aId; name = aName; }
	public String toString() { return id + ": " + name; }
	public void setName(String newName) { name = newName; }
}

public class Main {
	public static void main(String[] args)	{
		Employee e = new Employee("001", "Carl Cracker");
		e.setName("Helena");
		System.out.println(e); // [Output] 001: Helena
	}
}


static and non-static methods
=============================
class A {
	public int x1;
	public static int x2;

	
	public void m1() {

		m2();
	}

	public static void m2() {
		x2+=100;
	} 	
}

public class Main {

	public static void main(String[] args) {

		(new A()).m1(); 
		(new A()).m1();
	}
}

	// public static void m2() {

	// 	//x1+=100; //<== this is invalid. [line X1]
	// 	x2+=100;
	// 	//m1(); //<== invalid [line X2]
	// } 	


RandomNumber
============
class RandomNumber {

	private int r=(int)(Math.random()*100); //0..99
	
	public RandomNumber(int n) { r=(int)(Math.random()*n); }
	
	public String toString() {return ""+r;}
	
}

public class Main {

	public static void main(String[] args) {

		// System.out.println(new RandomNumber(1000)); //Expected: 0..999 [OK]
		// System.out.println(new RandomNumber()); //Expected: 0..99 [ERROR!]
	}
}


Basic Casting
=============

public class Main {
    public static void main(String [] args) 
    {	
            int i=97; char c;
            c=(char)i; 
            System.out.println(i); //output: 97
            System.out.println(c); //output: a
    }		
    
}


Inheritance and Casting
=======================
class A {
    public String f1() { return "A solution";}    
}

class B extends A {
    public String f1() { return "Best solution";}
}

public class Main {
    public static void main(String [] args) {	
            go(new B());
    }		
    
    public static void go(A x) {
        String result1 = ((B)x).f1(); //"A solution" or "Best solution"?
        String result2 = x.f1(); //"A solution" or "Best solution"?
        System.out.println(result1 + ", " + result2); 
    }
}


Up-casting, Down-casting
=================================
class A {
	private int x;
	public A() { x = 100; }
	public void m1() { System.out.println(x); }
}

class B extends A {
	private int y;
	public B() { y = 200; }
	public void m1() {System.out.println(y);}
}

public class Main {
	public static void main(String[] args) {
		A i = new A();
		B j = new B();

		// Testing
		i.m1();
		j.m1();
		((A)j).m1();
		((B)i).m1();
		
		// B k = (B)i;  // <=== error here?
		// k.m1();      // <=== error here?
	}
}


Object, Casting
================
public class Main {
    public static void main(String[] args) {
        Integer i=3;	//line 1
   
        String s;		//line 2
        s = (String)i;	//line 3
        
        Object o;		//line 4
        o = i;			//line 5
        i = (Integer)o;	//line 6     
    }
}


for-each loop, Integer, ArrayList
=================================
import java.util.*;

public class Main {
    public static void main(String[] args) {

        Integer[] arr = new Integer[3]; // Simply treat Integer as int (See Topic 04)
        arr[0] = 100;
        arr[1] = 101;
        arr[2] = 109;

        ArrayList<Integer> alist = new ArrayList<Integer>();
        alist.add(100);
        alist.add(101);
        alist.add(109);

        for (int i = 0; i < arr.length; i++)
            System.out.print(arr[i] + " ");

        System.out.println();

        for (int i = 0; i < alist.size(); i++)
            System.out.print(alist.get(i) + " ");

    }
}


for-each loop, Run-time Problem : ConcurrentModificationException
==================================================================
import java.util.*;

public class Main {
    public static void main(String[] args) {

        Integer[] arr = new Integer[3]; // Simply treat Integer as int (See Topic 04)
        arr[0] = 100;
        arr[1] = 101;
        arr[2] = 109;

        ArrayList<Integer> alist = new ArrayList<Integer>();
        alist.add(100);
        alist.add(101);
        alist.add(109);

        // printing using toString
        System.out.println(Arrays.toString(arr)); // output: [100, 101, 109]
        System.out.println(alist.toString()); // output: [100, 101, 109]
        System.out.println();
        System.out.println();

        // Try to change element values
        for (Integer e : arr)
            e++;

        for (Integer e : alist)
            e++;

        System.out.println(Arrays.toString(arr)); // output:____________________
        System.out.println(alist.toString()); // output:____________________
        System.out.println();
        System.out.println();

        // Try to change add or remove element in arraylist
        for (Integer e : alist) {
            if (e == 109)
                alist.add(110);
        }

        for (Integer e : alist) {
            if (e == 109)
                alist.remove(e);
        }

        System.out.println(Arrays.toString(arr)); // output:____________________
        System.out.println(alist.toString()); // output:____________________

    }
}