Question

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package javaapplication1;
 import java.io.*;
/**
 *
 * @author simon
 */
public class Main {


    /**
     * @param args the command line arguments
     */
       public static void main(String[] args) throws IOException {
            NotSimple[] objArray;
               BufferedReader stdin = new BufferedReader(
                                   new InputStreamReader( System.in ) );
            System.out.println( "Enter a number of objects:" );

            int size;
            size = Integer.parseInt( stdin.readLine() );

            //Initialize objArray
            objArray = new NotSimple[size];

            //TODO: Implement following functions

            initializeObj(objArray);
            increaseData(objArray);
            printObjData(objArray);

            //TODO: Explain all outputs of the below function
            explainOutputs();
            return;

                                                                 }

      //TODO
      //initialize every Notsimple object in the array 'a'
      //to NotSimple()
      //Hint: using the for loop, assign a[i] = new NotSimple();
      static void   initializeObj(NotSimple[] a){
      //TODO: FILL ME

          for (int i = 0; i < a.length; i++)
          {
          a[i] = new NotSimple();
          }

  }

  //TODO:
  //Increase the ‘data’ member of every NotSimple object
  //in the array ‘a’ by 1
  static void increaseData(NotSimple[] a) {
       //TODO: FILL ME

      for (int i = 0; i < a.length; i++)
      {
           a[i].setData(a[i].getData()+1);

      }

  }

  //TODO:
  //Print the data of every NotSimple object in the array ‘a’
  static void printObjData(NotSimple[] a) {
       //TODO: FILL ME
       for (int i = 0; i < a.length; i++)
          {
          System.out.println (a[i].getData());
          }

  }

  //TODO explain all the outputs 1a-1f
  static void explainOutputs() {
    NotSimple nsObj1 = new NotSimple();
    //1a
    System.out.println( "nsObj1.data is\t" + nsObj1.getData() );
    System.out.println( "nsObj1.str is \t" + nsObj1.getStr() );

    NotSimple nsObj2 = new NotSimple( 50,
                         "Another immutable string!" );
    //1b
    System.out.println( "nsObj2.data is\t" + nsObj2.getData() );
    System.out.println( "nsObj2.str is \t" + nsObj2.getStr() );

    nsObj2 = nsObj1;

    nsObj2.setData(10);
    nsObj1.setData(100);
    //1c
    System.out.println( "nsObj2.data is\t" + nsObj2.getData() );
    System.out.println( "nsObj2.str is \t" + nsObj2.getStr() );

    nsObj1 = new NotSimple();
    //1d
    System.out.println( "nsObj1.data is\t" + nsObj1.getData() );
    System.out.println( "nsObj1.str is \t" + nsObj1.getStr() );
    System.out.println( "nsObj2.data is\t" + nsObj2.getData() );
    System.out.println( "nsObj2.str is \t" + nsObj2.getStr() );

    nsObj2 = new NotSimple();
    //1e
    System.out.println( "nsObj2.data is\t" + nsObj2.getData() );
    System.out.println( "nsObj2.str is \t" + nsObj2.getStr() );

    nsObj2.setData(10);
    //1f
    System.out.println( "nsObj1.data is\t" + nsObj1.getData() );
    System.out.println( "nsObj1.str is \t" + nsObj1.getStr() );
    System.out.println( "nsObj2.data is\t" + nsObj2.getData() );
    System.out.println( "nsObj2.str is \t" + nsObj2.getStr() );
  }

}


class NotSimple
{
  NotSimple()
  {
    data = 5;
    str = new String( "Initialized!" );
  }

  NotSimple( int i, String str1 )
  {
    data = i;
    str = str1;
  }

  void setData( int i )
  {
    data = i;

    return;
  }

  int getData()
  {
   return data;
  }

  void setStr( String str1)
  {
    str = str1;

    return;
  }

  String getStr()
  {
    return str;
  }

  private int data;
  private String str;
}

The instructor wants me to “Increase the ‘data’ member of every NotSimple object in the array ‘a’ by 1” When I run the program it only increases the first data. For example when I enter 3 I get this:

run:

Enter a number of objects:
3
6
6
6
nsObj1.data is        5
nsObj1.str is         Initialized!
nsObj2.data is        50
nsObj2.str is         Another immutable string!
nsObj2.data is        100
nsObj2.str is         Initialized!
nsObj1.data is        5
nsObj1.str is         Initialized!
nsObj2.data is        100
nsObj2.str is         Initialized!
nsObj2.data is        5
nsObj2.str is         Initialized!
nsObj1.data is        5
nsObj1.str is         Initialized!
nsObj2.data is        10

My question is shouldn’t all the data be increased by 1? i.e. 101, 6, 101, 6, 6, 11

Answer 1

You have two main operations here. The first is the creation of an array containing x elements, each of this element is initialized with the value 5 and get incremented by one. This give you this result :

3
6
6
6

3 elements, with the value 5, incremented.

The second part of your code (the explainOutputs()) doesn’t increment anything. Two objects are declared (nsObj1 and nsObj2), and they’re modified manually before you print them. No incrementation. It just print what you’ve set.

Here is what you’ve done :

1. NotSimple nsObj1 = new NotSimple();
   prints 5.
2. NotSimple nsObj2 = new NotSimple(50, "Another immutable string!");
   prints 50
3. nsObj2 = nsObj1; nsObj2.setData(10); nsObj1.setData(100);
   Basically you just said that nsObj2 value is 100 and it prints 100
4. nsObj1 = new NotSimple();
   nsObj1 will print 5 (as it’s a reference to a new Object)
   nsObj2 will still print 100
5. nsObj2 = new NotSimple();
   nsObj2 is a reference to a new Object, it will print 5
6. nsObj2.setData(10);
   nsObj1 still prints 5
   nsObj2 will print 10 for because only the object referenced by nsObj2 will have a value changed

Result :
5 50 100 5 100 5 5 10