How to write an Iterator for a custom class in Java

Question

I have this class:

public class MyClass{
   private Test test;

   public class Test{
     int num;
     String color;

     public Test(int num, String color){
     this.num = num;
     this.color = color;
     }
   }

   public MyClass(){

   }

   public void setNum(int number){
       test.num = number;
   }

   public void setColor(String color){
       test.color = color;
   }

   public Test getTest(){
       return test;
   }
}

I am setting the values from another class and at the end I call the method getTest:

MyClass myclass = new MyClass();
.
.    
.
Test test1 = myclass.getTest();

I want to Iterate the object test1 to get the values. Is that possible? Do I have to implement hasNext() method inside the class MyClass? If yes, how can I do it?

They're off different types - what are you actually trying to achieve here? (i.e. what do you want to do with this hypothetical iterator?) — Oliver Charlesworth, Dec 30 '15 at 00:49
Why would you use an Iterator to do that? There's one int and one string. They're not conceptually a sequence. They're not even the same type! Just use `test1.num` and `test1.color`. — user2357112, Dec 30 '15 at 00:49
I know they are different types, that's why I need an answer. I am trying to save me time. — dirac, Dec 30 '15 at 00:49
@user2357112 In my original code, I have 100 fields, not just 2. — dirac, Dec 30 '15 at 00:53
@dirac: We can't give you a meaningful answer without *context*. What is your goal here? — Oliver Charlesworth, Dec 30 '15 at 00:56

score 0 · Accepted Answer · edited May 23 '17 at 10:27

0

You question has already been asked and answered.

Basic idea - you need to use reflection API . E.g construction test.getClass().getDeclaredFields();

Note: you will not create iterator this way, but you will be able to iterate through class fields. That slightly different things.

edited May 23 '17 at 10:27

Community

1
1

answered Dec 30 '15 at 00:55

Dmitry

1,263
11
15

score 0 · Answer 2 · answered Dec 30 '15 at 02:08

You want this？

public static void main(String[] args) {

    MyClass myclass = new MyClass();
    Test test1 = myclass.getTest();
    //you need modify private Test test = new Test(1, "hahs");
    //import java.lang.reflect.Field;
    Field[] fields = test1.getClass().getDeclaredFields();
    for (int j = 0; j < fields.length-1; j++) {
        fields[j].setAccessible(true);
        try {
            System.out.println(fields[j].get(test1));
        } catch (IllegalArgumentException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    //output
    //1
    //hahs
}

score -1 · Answer 3 · answered Dec 30 '15 at 00:52

You will have to use reflection in order to iterate through the members of the test class. You will have to import java.lang.reflect.* and call Class.forName("test1) to get a Class object, and call the getDeclaredFields method of the Class object to get an array of Field objects. The Field object has get and set methods that get or set the value of the field.

How to write an Iterator for a custom class in Java

3 Answers3