Java检索数组并在for每个循环中打印

Question

I am trying to make a program where it retrieves a set of arrays from a different class

int barHeights[] = new int[]
{ 1, 2, 3, 4, 5, 6, 7 };

then calling it in a method and printing it out

public void init(int[] barHeights)
{
    Bar[] barArray = new Bar[barHeights.length];
    for (Bar bar : barArray){
        System.out.println(bar);
}

i'm unsure why it is printing out 'null' 7 times in a row in the console. Shouldn't it be:

1
2
3
4
5
6
7

Answer 1

In line:

Bar[] barArray = new Bar[barHeights.length];

You are creating an instance of array of Bar class references instead of int.
This array is automaticly initialized with null values, and in line:

for (Bar bar : barArray){
    System.out.println(bar);

You are interating those null values.
If you want to retrive the array, which you passed as an argument to method, you should use:

public void init(int[] barHeights) {
    for (int i : barHeights) {
        System.out.println(i);
    }
}

Answer 2

you have created arry Bar but not initialized it, so it is initialized with null.

Bar[] barArray = new Bar[barHeights.length];

when you loop through barArray

for (Bar bar : barArray){
    System.out.println(bar);

it will display null.

Answer 3

Code should be like this.

class Bar {
    private int height;

    public int getHeight() {
        return height;
    }

    public void setHeight(int height) {
        this.height = height;
    }
}

Algorithm should be like this

1.create another array type of Bar named barArray.

2.loop height array named barHeights

3.within loop create new object of Bar for each round

4.set height for each object

5.add bar object to array

public void init(int[] barHeights)
{
    Bar[] barArray = new Bar[barHeights.length];
    int index=0;
    for (int height : barHeights){
        Bar bar=new Bar();
        bar.setHeight(height);
        barArray[index]=bar;
        index++;
        System.out.println(bar);
    }
}