Retrieving elements from a Dynamic array

Question

Preface

I'm trying to implement a Dictionary data structure that stores Pairs(an object) in a dynamic array.

The array starts off with size [10]. Every time the user tries to add another Pair to the Dictionary when the array is full; the dynamic array increments the length of the array by 5.

There are 3 relevant methods.

put: Adds a pair to the dynamic array

dynamicArray: Increases the size of the array when full

get: Retrieves a specific element from the array

Problem

When the dynamicArray is called to be initialized with many elements, the elements don't seem to be properly stored. When trying to get the elements, it catches a NoSuchElementException which indicates the values were not stored in the first place. Here is the relevant code, thank you.

public Token get (String key) throws NoSuchElementException,
                                         NullPointerException{
        boolean found=false; //Represents if pair is found
        Token token = null;
        if (key ==null)
            throw new NullPointerException ();

        for (int i=array.length-1; i>=0; i--){
            if ( array[i]!=null && array[i].getKey() == key){
                found=true;
              return (array[i]).getToken(); 


            }   
        }
        if (found!=true)
            throw new NoSuchElementException ();
            return  token;

        }

private void dynamicArray(){
        if (array[array.length-1]!=null){
            Pair[]replace = new Pair[array.length+5];
            System.arraycopy(array, 0, replace, 0, array.length);
            array=replace;
        }
    }

public void put  (String key, Token value) throws NullPointerException{


        if (key == null || value == null)
            throw new NullPointerException ();

        dynamicArray();
        Pair p1 = new Pair (key,value);

        for (int i=0; i<array.length; i++){
            if (array[i]== null ){
                dynamicArray();
                array[i]=p1;

                break;

            }   
            }   
    }

TestCase

@Test()
    public void testPutDyncamicArray() {
        System.out.println("test: testPutDyncamicArray");
        Dictionary dict = new Dictionary();
        for (int i = 0; i < 1000; i++) {
            dict.put("X" + i, new Token(i));
        }
        for (int i = 0; i < 1000; i++) {

            Assert.assertEquals(new Token(i), dict.get("X" + i));
        }
    }

We're limited to using Dynamic arrays. array represents an array of Pairs. A pair consists of a (String,Token) — Jusgud, Mar 23 '15 at 16:38
Also note that using `==` with `String` is wrong and that is probably the issue here. — , Mar 23 '15 at 16:38
possible duplicate of [How do I compare strings in Java?](http://stackoverflow.com/questions/513832/how-do-i-compare-strings-in-java) — , Mar 23 '15 at 16:41

score 5 · Accepted Answer · answered Mar 23 '15 at 16:41

5

Since your keys are String, you need to use the equals method for checking key equality:

if (array[i] != null && array[i].getKey().equals(key)){
    return array[i].getToken(); 
}

answered Mar 23 '15 at 16:41

Jean Logeart

52,687
11
83
118

score 0 · Answer 2 · answered Mar 23 '15 at 16:35

0

You'll find that a HashMap (or just a Map) will do what you want with a lot less effort.

answered Mar 23 '15 at 16:35

Luis Figueiredo

91
3

This question sounds like a [tag:homework] question. – Powerlord Mar 23 '15 at 16:50

Retrieving elements from a Dynamic array

2 Answers2