Armel Moukoss

Thank you Alejandro for your help, but i am still confused. I would be glad to receive others helps. Thank you.

Armel

Hello,

i need your help, i don't understand the output of this code. Can you help me please ?

<CODE>
class Parent
{
private void method1() // the method is private
{
System.out.println("Parent's method1()");
}
public void method2()
{
System.out.println("Parent's method2()");
System.out.println(this);
method1();
}
}

class Test extends Parent
{
public void method1()
{
System.out.println("Test's method1()");
}
public static void main(String args[])
{
Parent p = new Test();
p.method2();
}
}
</CODE>

I have this as output in my computer :

Parent's method2()
Test@18d107f
Parent's method1()

I think, it shoul be :

Parent's method2()
Test@18d107f
<BOLD> Test's method1() </BOLD> because the object executing method2() is Test@18d107f

Thank you very much.

Armel

Hi everyone,
I don't understand why this code produce this result : d a .
I think, il would be : d d. Thank you for your help.

Armel

class Animal { static void doStuff() { System.out.print("a "); } } class Test extends Animal { static void dostuff() { // it's a redefinition, // not an override System.out.print("d "); } public static void main(String [] args) { Test t = new Test(); t.dostuff(); t.doStuff(); } }

Hi Olivier,

Firstly congratulation for your amazing score !!! I am in paris and i would take the exam for the end of month, but i don't know which is the best exam center in Paris. Which exam center did you take the SCJP ?
Thank you for your answer and the tips you gave in your previous post.

Armel

Thank you Manfred Klug for your help.

Armel

I have another question if i delete the notify() method in class ThreadB i have the same result. I thought that without notify in class ThreadB, the class ThreadA will still wait. ThreadA complete his synchronized code without any problems.

Do you have any answer for this question ? Thank you.

Armel

thank you guys for your help !!!

Armel

hi,

I need your help, I don't understand the way this code works.
I thought that after writting b.start(); the code within the run() method
will be excuted.But it's excuted only later in synchronized.why ?


public class ThreadA { public static void main(String[] args){ ThreadB b = new ThreadB(); System.out.println("total value before the start method :" + b.getTotal()); b.start(); // I thought it will execute the code within run method here System.out.println("total value after the start method :" + b.getTotal()); synchronized(b){ try{ System.out.println("Waiting for b to compl�te .."); b.wait(); System.out.println("After the wait"); }catch (InterruptedException e){} System.out.println("Total is : " + b.total); } } } public class ThreadB extends Thread { public int total; public int getTotal(){ return total; } public void run(){ System.out.println("***********In the run method****************"); synchronized(this){ for (int i=0;i<100;i++){ total +=i; } notify(); } System.out.println("***************End of the run method******************"); System.out.println("total value in synchronized method :" + getTotal()); } }



This is the output :

total value before the start method :0
total value after the start method :0
Waiting for b to compl�te ..
***********In the run method****************
After the wait
Total is : 4950
***************End of the run method******************
total value in synchronized method :4950

I have looked for in the old posts and i find one about this problem but the answer wasn't clear. Thank you for your help.

Armel

Thank you Mar for your help.

Armel

Hi everyone,
Can someone, please, explain me why I have a running error with this code :

import java.util.*; public class Test{ public String name; Test(String n){ name = n;} public static void main(String args[]){ List <Test> d = new ArrayList<Test>(); Iterator<Test> i3 = d.iterator(); // (1)If i put this line in commentary and Test test = new Test("aiko"); d.add(test); d.add(new Test("clover")); d.add(new Test("magnolia")); //Iterator<Test> i3 = d.iterator(); (2) remove commentary here, I don't have any runnig compil while (i3.hasNext()){ Test d2 =i3.next(); // running error here !!! System.out.println(d2.name); } System.out.println("size " + d.size()); System.out.println("get1 " + d.get(1).name); System.out.println("aiko " + d.indexOf(test)); d.remove(2); Object[] oa = d.toArray(); for (Object o : oa){ Test d2 = (Test)o; System.out.println("oa " + d2.name); } } }
the error is :

Exception in thread "main" java.util.ConcurrentModificationException
at java.util.AbstractList$Itr.checkForComodification(Unknown Source)
at java.util.AbstractList$Itr.next(Unknown Source)
at Test.main(Test.java:21)

Thank you for your help.

Armel

Edit by mw: Fixed code tags. (Tags in these forums use square brackets [] instead of angled brackets.)
[ June 20, 2007: Message edited by: marc weber ]

Hi,

Just to thank you very much guys for yours answers.

Armel

Hi,

I don't really understand how the toString method is used in the code below :
import java.util.*; // // This class implements a vector of characters, capable of sorting // and reversing itself. // public class CleverVector extends Vector<Character> { // Initializes this object with nChars unique characters. public CleverVector(int nChars) { while (size() < nChars) { Character c = randomChar(); if (!contains(c)) // Don't add any duplicates add(c); } } // // Returns a random character in the range A-Z, a-z. // private static Character randomChar() { boolean uppercase = (Math.random() > 0.5); char base = uppercase ? 'A' : 'a'; int rand = (int)(26 * Math.random()); // 0 - 25 char c = (char)(base + rand); // A-Z or a-z return c; // Autoboxed } // // Sorts the contents of this vector, by copying the elements into // a TreeSet, then retrieving them in sorted order. // public void sort() { // Copy contents into sorting set. TreeSet<Character> sorter = new TreeSet<Character>(); for (Character ch:this) sorter.add(ch); // Remove contents of this vector. clear(); // Retrive set contens in sorted order, and add them to this vector. for (Character ch:sorter) add(ch); } // // Reverses the contents of this vector, by copying the elements into // another Vector, then retrieving them in reverse order. Enhanced-for // isn't helpful here, but copying the elements into the other Vector // is easy because there's a copying constructor. // public void reverse() { // Copy this vector. Vector<Character> otherVec = new Vector<Character>(this); // Copying constructor // Remove contents of this vector. clear(); // Retrieve from otherVec in reverse order. for (int i=otherVec.size()-1; i>=0; i--) add(otherVec.get(i)); } public String toString() { String s = ""; for (Character c:this) s += c.charValue(); return s; } public static void main(String[] args) { int nChars = Integer.parseInt(args[0]); CleverVector vec = new CleverVector(nChars); System.out.println("Initial State: " + vec); vec.sort(); System.out.println(" Sorted: " + vec); vec.reverse(); System.out.println(" Reversed: " + vec); } }
One of the possible result :


Initial State: [k, q, i, j, f, V, J, S, c, v, u', U, C, z, I, y, d, H, X, e]
Sorted: [C, H, I, J, S, U, V, X, c, d, e, f, i, j, k, q, u', v, y, z]
Reversed: [z, y, v, u', q, k, j, i, f, e, d, c, X, V, U, S, J, I, H, C]



I don't see any place where the toString method is called. But if i put it in commentary the result is not the same. Can someone help me, please ? thank you.

Ps : I take the code on the cd of the book "complete java 2 certification", in solution of the chapter 8.

Thank you to everyone for your answer. I thought that the equals method was the same for Object, Integer,.. and so one. But i was wrong. thank you !!!

Hi everybody,
Can anyone explains the result of this code :

public class Reference {
public static void main (String Args [] ){
Reference t1 = new Reference ();
Reference t2 = new Reference ();

if (t1.equals(t2)){
System.out.println ("Same content");
}else{
System.out.println ("Different content");
}
}
}
the output is : Different content. I thought it would be Same content.
Thank you