Printing an array with no elements?

Question

I have a few questions. I am working on a homework assignment but came across a few confusing things. (I am taking an introductory class, sorry for the mistakes.)

Implement a class that takes an integer array and an int x as its size. Create a method inside the class that creates a new array whose length is one greater than data’s length. Then create a method to copy all data’s elements into the new array and add the value of x into the last element of the array. Create a method to return all the integers in the new array.

Here's what I have

package taskone;

import java.util.*;

class Arrayplus1 {

    int x;
    int data[];

    void example(int x) {
        this.x = x+1;
        this.data= new int[x];
    }

    void increaseSizeOfArray(int incrementSize) {
            int copiedArray[] = Arrays.copyOf(data, data.length + incrementSize);
            data = copiedArray;

    }

    void printall() {
        System.out.println(Arrays.toString(data));
    }
}

public class TaskOne {

    public static void main(String[] args) {
        example task = new example();
        task.printall();
    }

}

This simply returns null.

My question is the last bit of the task above. "Create a method to return all the integers in the new array."

How is this possible when I did not include any elements in my array? I am trying to follow the assignment guidelines. Thanks.

It seems that you tried to fulfill the last requirement with your printall method. But the requirement is to return all the integers and not to print them. Additionally, you even did not correctly implement the first requirement. — Seelenvirtuose
add the value of x into the last element of the array - you are supposed to add x to the array, so it won't be empty. — Eran
I suggest you start with an empty array instead of null i.e. int[] data = { }; — Peter Lawrey
new example() creates an object of the class example, and I don't see a class named example. — ajb
The assignment says "Implement a class that takes an integer array and an int x as its size". To me, this means that one of the constructor parameters is an integer array that already has data in it. The method in the third sentence is supposed to copy this data into the new array. — ajb

Ian2thedv Ian2thedv · Accepted Answer · 2015-04-21T06:52:15

Implement a class that takes an integer array and an int x as its size.

You can accomplish this by the use of a constructor. You can save the arguments passed to the constructor as private variables and reference by using the this notation. (See this)

public class TaskOne {
    private int [] array;
    private int x;
    public TaskOne(int [] array, int x) {
        this.array = array;
        this.x = x;
    }
}

Create a method inside the class that creates a new array whose length is one greater than data’s length

Here you need to simply create a new array. Be sure you set the length of the new array to that of array, plus 1 (to accommodate the extra element, x)

private int [] data = null;

public void createNewArray() {
    this.data = new int[this.array.length + 1];
}

Then create a method to copy all data’s elements into the new array and add the value of x into the last element of the array.

public void populateArray() {
    for (int t = 0; t < this.array.length; t++) {
        data[t] = this.array[t];
    }
    data[array.length] = this.x;
}

Create a method to return all the integers in the new array

This is know as a getter method. You

public int [] getClone() {
    return this.data;
}

You may have noticed that I did not make use of the Arrays.copyOf method. This actually creates and populates the array in one step, so, I kept the two steps separate to conform to the question.

Printing an array with no elements?

2 Answers