Int value does not change after calling method

Question

After calling doReading(),the value of pages is supposed to change, but it does not. Is it possible to do this without declaring int pages; in the MyMath2 and MyScience2 classes. The output should be something like: Before reading: Math- must read 5 pages After reading: Math- must read 3 pages

Abstract Homework2

 public abstract class Homework2 implements Processing
{
  private int pagesToRead;
  private String typeHomework;

 {
    // initialise instance variables
    pagesToRead = 0;
    typeHomework = "none";
 }

 public Homework2(int pages, String hw)
 {
    pagesToRead = pages;
    typeHomework = hw;
 }

 public abstract void createAssignment(int pages);

 public int getPages() 
 {
    return pagesToRead;
 }

 public void setPagesToRead(int p) 
 {
    pagesToRead = p;
 }

 public String getTypeHomework() 
 {
    return typeHomework;
 }

 public void setTypeHomework(String hw)
 {
    typeHomework = hw;
 }

 public String toString() 
 {
    return "reading: \n" + typeHomework + " - must read " + pagesToRead + " pages";
 }

}

TestHomework2

public class TestHomework2
{

public static void main(String []args)
{   

  List<Homework2> tester = new ArrayList<Homework2>();

 tester.add( new MyMath2(5, "Math"));                 
 tester.add( new MyScience2(7, "Science"));


 for (Homework2 c: tester)
  {
    System.out.print("Before ");
    System.out.println(c);
    c.doReading();
    System.out.print("After ");
    System.out.println(c); 
  }


}
}

Interface Processing

public interface Processing
{
 void doReading()
}

MyMath2

 public class MyMath2 extends Homework2 implements Processing
 {
  int pages; 

 public MyMath2(int pages, String hw)
 {
    super(pages,hw);
 }

 public void createAssignment(int pages) 
 {
    setTypeHomework("Math");
    setPagesToRead(pages);
 }

 public void doReading()
 {
   pages = pages - 2;
 }
 }

MyScience2

public class MyScience2 extends Homework2 implements Processing
{
   int pages;

 public MyScience2(int pages, String hw)
 {
    super(pages,hw);
 }

 public void createAssignment(int pages) 
 {
    setTypeHomework("Science");
    setPagesToRead(pages);
 }

 public void doReading()
 {
  pages = pages - 3; 
 }
}

You are never changing the variable pagesToRead, are you? – Anil Feb 07 '15 at 17:45 — Anil, Feb 07 '15 at 17:45

score 1 · Accepted Answer · answered Feb 07 '15 at 17:44

1

Fields are not overridden. This means that the initial pagesToRead won't get updated when doReading() is called, since that method changes pages.

You should just do:

public void doReading(){
    setPagesToRead(getPages() - 2);
}

answered Feb 07 '15 at 17:44

Obicere

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score 1 · Answer 2 · answered Feb 07 '15 at 17:45

System.out.print("After ");
System.out.println(c);

class the toString() of Homework2

public String toString() 
{
     return "reading: \n" + typeHomework + " - must read " + pagesToRead + "     pages";
}

there you return the pagesToRead. But in doReading you reduce pages not pagesToRead:

public void doReading()
{
     pages = pages - 2; 
}

reduce pagesToRead:

public void doReading()
{
     pagesToRead = pagesToRead - 2; 
}

score 1 · Answer 3 · answered Feb 07 '15 at 17:46

When you change the page count by calling doReading, you are changing the value of pages in MyMath2 object (property of MyMath2 object). And the number that you are printing is coming from Homework2.pagesToRead field.

This field in Homework2 is never changed when you call doReading method and hence you get the same value. You could fix this by setting the value that you set in MyMath2 object like:

public void doReading(){
    pages = pages - 2;
    super.setPagesToRead(pages);
}

Or you completely remove pages field from MyMath2 and use field from parent object like:

public void doReading(){
    super.setPagesToRead(super.getPagesToRead() - 2);
}

Same applies to MyScience2 class as well.

Int value does not change after calling method

3 Answers3