Iterator to call class function in java

Question

package test_run;

import java.util.ArrayList;
import java.util.Iterator;

class Al_class
{
  int x;

  Al_class() {
    x=0;
  }

  void increment(){
      ++x;
  }

  int get_value(){
      return x;
  }

    ArrayList<Al_class> class_declare(){
    //void class_declare(){
      Al_class alc1 = new Al_class();
      Al_class alc2 = new Al_class();
      Al_class alc3 = new Al_class();
      alc1.increment();
      alc1.increment();
      alc1.increment();
      alc2.increment();

      ArrayList al = new ArrayList();
      al.add(alc1);
      al.add(alc2);
      al.add(alc3);
      return al;
  }



} ///:~

class Main
{

  public static void main(String[] args) {
    Al_class a = new Al_class();
    ArrayList<Al_class> b;

    b=a.class_declare();
    a.class_declare();
    System.out.print(" Arraylist size= "+ b.size());

    for (Al_class c : b ){

        System.out.print("\n" + c.get_value() + "\n");
    }
    b.remove(0);
    System.out.print(" Arraylist size= "+ b.size());

    Iterator it= b.iterator();
    while (it.hasNext()) {
        System.out.print("\n" + it.next());
        // Al_class e=it.next();
        // System.out.print("\n" + e.get_value());          
    }
  }
}

How can I use iterator to call the object function get_value? Its not a homework, but self learning.

Why did you comment out the correct answer (in the while (it.hasNext()) method). — Buhake Sindi
– Buhake Sindi, Commented Jun 1, 2011 at 13:42

Joachim Sauer · Accepted Answer · 2011-06-01 13:53:53Z

2

You must use generics, which means to change Iterator to Iterator<A1_class>:

Iterator<A1_class> it= b.iterator();
while (it.hasNext()) {
    Al_class e=it.next();
    System.out.print("\n" + e);
    System.out.print("\n" + e.get_value());          
}

edited Jun 1, 2011 at 13:53

answered Jun 1, 2011 at 13:41

Joachim Sauer

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2 Comments

Buhake Sindi Over a year ago

you are calling it.next() twice so, A1_class e will return a every 2nd element from the iterator and print the odd items in sysout.

Joachim Sauer Over a year ago

@TheElite: thanks for notifying me, I simply uncommented the code from the sample ;-) Oh, the dangers of copy-and-paste!

nsfyn55 · Accepted Answer · 2011-06-01 14:05:44Z

0

You can approach a few ways

Explicit Cast

while (it.hasNext()) {
    Object o = it.next();
    if(o instanceof Al_class){
        Al_class e=(Al_class)o;
        System.out.print("\n" + e.get_value());  
    } 
}

Generics

Iterator<A1_class> it= b.iterator();
while (it.hasNext()) {
    Al_class e=it.next();
    System.out.print("\n" + e.get_value());          
}

Your not really supposed to do explicit casting w/ type checking anymore, but its still in there and has limited use cases.

edited Jun 1, 2011 at 14:05

answered Jun 1, 2011 at 13:59

nsfyn55

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