具有返回数组的参数的类方法

Question

I'm pretty new to Java and not from a programming background. I am doing a course and am stuck on a piece I hope this is appropriate to ask a question here). The question ask to create a method that takes an array of integers as an argumetn and returns a sorted set containing the elements of the that array. I am not including the code as I don't want the answer but I would like a clue. It's driving me nuts!

Yours in anticipation

JC

Answer 1

Ok, let's go through this together. Follow me:

The question ask to create a method that takes an array of integers as an argumetn and returns a sorted set containing the elements of the that array.

We have three steps here:

1. we need to figure out how to pass an array to a function
2. we need to figure out how to sort elements
3. we need to figure out how to return an array (of sorted elements)

What I'm doing here is taking the main problem and dividing it into smaller, more approachable sub-problems. It's called divide et impera . You'll encounter this approach very often if you pursue a programming career.

1. pass an array to a function: write a simple program that prepares an array, passes it to a function and have the function print it. Something like (in my own just-made up version of a pseudocode):

 main() { a[] = { "one", "two", "three"}; f(a); } f(arr[]) { for ( int i = 0 ; i < arr.length ; i++ ) print(arr[i]); } 

You with me so far? I hope so.

Now,

2. sorting of elements: I'm pretty sure you already have a way of doing it in your textbook or your notes. Remember you must sort an array. Now our function f() would look something like:

 f(arr[]) { /* insert here your sorting method */ } 

Once this is done, you need to pass back this array to the main function. Now, if you were to pass back a single value from a function, you would do something like:

 int g() { int i = 0; i++; return i; } 

since they want you to return an array, it would be something like:

 int[] h() { /* initialize the array */ int[] j = { 1, 2, 3 }; /* your code goes here */ return j; } 

At this point you have all elements you need for the question you were asked. Just make them work in java first , then put everything together.

Welcome to the magic world of programming :)

Answer 2

Tips:

1. How do you create an element that takes an int as an argument?
2. How do you declare an array of type int ?
3. Put those together.

For the SortedSet :

1. Convert the array to a List . Hint: look for an asList() method
2. Add all the elements of the resulting List to a SortedSet . Hint: addAll() .

EDIT: Aaargh! Didn't see the SortedSet in the question

Answer 3

import org.junit.Test;

import java.util.Arrays;
import java.util.SortedSet;
import java.util.TreeSet;

import static org.hamcrest.CoreMatchers.instanceOf;
import static org.hamcrest.Matchers.greaterThan;
import static org.hamcrest.core.Is.is;
import static org.junit.Assert.assertThat;

/**
 * @version $Id$
 */
public class MainTest {

    public SortedSet sortIntegers(Integer[] ints) {
        return new TreeSet(Arrays.asList(ints));
    }

    @Test
    public void it_should_return_a_sorted_set() throws Exception {
        assertThat(sortIntegers(new Integer[]{5, 7, 1, 6}), is(instanceOf(SortedSet.class)));
    }

    @Test
    public void it_should_return_four_elements() throws Exception {
        assertThat(sortIntegers(new Integer[]{5, 7, 1, 6}).size(), is(4));
    }

    @Test
    public void it_should_return_in_the_right_order() throws Exception {
        Integer previous = 0;

        for (Integer current : sortIntegers(new Integer[]{5, 7, 1, 6})) {
            assertThat(current , is(greaterThan(previous)));
            previous = current;
        }        
    }

}

Answer 4

There are plenty of tutorials on the net, check out this example , its not exactly what you want but may point you in the right direction.

Good Luck!

Answer 5

You can create a new array, and iterate over your given array as long as there are still ints in your array. You can search for the highest or lowest int and put this one in the new array, and remove it from the given array. You can do this as long as there are items in the given array. If the given array is empty return the new array.

I thought this is what you meant.

---

I did not read properly, sorry.

You can create a new SortedSet, see here for more information: SortedSet , and use add or addAll to add items to this sortedSet. See for more information about Set

Answer 6

There are some points you should remember:

SortedSet is an interface, so you must find a suitable implementation (Hint: the API contains "All Known Implementing Classes")

The "int"s are native datatypes, no objects. So you need to encapsulate them in wrappers (see Integer.valueOf() ) before you can use them in a Set.

The rest should be a simple iteration over the source array, and putting each element to the new Set.

HTH