我无法阻止 null 出现在我的 output 中，用于我在 java 中的一维数组

Question

I am struggling to declare i as an interger and I can't figure out why the output is coming out as null. The goal is to make a sequence My code is:

public static void main(String[] args) {
        String[] myArray = new String[10];

        for (int i = 0; i < 10; i++) {
            for (int j = 0; j <= i; j++) {
                myArray[i] = myArray[i] + "A";
            }
            System.out.println(myArray[i]);
        }
    }

Answer 1

The problem is that none of the items inside the array has value, therefore they are null . You can use the following code which initialize all item whith an empty string in the first loop:

for (int i = 0; i < 10; i++) {
    myArray[i] = "";
    for (int j = 0; j <= i; j++) {
        myArray[i] = myArray[i] + "A";
    }
    System.out.println(myArray[i]);
}

Answer 2

public static void main(String[] args) { 
String[] myArray = new String[10];
for (int i = 0; i < 10; i++) {
    for (int j = 0; j <= i; j++) {
        myArray[i] = myArray[i] + "A";
    }
    System.out.println(myArray[i]);
    }
}

At this line

myArray[i] = myArray[i] + "A";

myArray[i] at the right side is null, so concatinating "A" with a null will make it null again. You should initialize each myArray[i] as Answered by Amir MB or can try this:

public static void main(String[] args) { 
String[] myArray = new String[10];
for (int i = 0; i < 10; i++) {
    for (int j = 0; j <= i; j++) {
        myArray[i] = "A" + myArray[i];
    }
    System.out.println(myArray[i]);
    }
}

Answer 3

for (int i = 0; i < 10; i++) {
    myArray[i] = "";
    for (int j = 0; j <= i; j++) {
        myArray[i] = myArray[i] + "A";
    }
    System.out.println(myArray[i]);
}


String[] myArray = new String[10];

This is an object array and all objects are initialized to null, if there is no explicit value assigned to it.

So, each element of the array needs to be assigned to a empty string; do it in the first for loop as mentioned above.

Or, assign values during array declaration itself. Worth for a small sized array, but won't recommend for a larger one.

String[] myArray = new String[]{"", "", "", "", "", "", "", "", "", ""};

Arrays class has a fill method.

String[] myArray = new String[10];
Arrays.fill(myArray, "");