Filling arrays
- Java course
- Beginner
- Lesson 55/116
- 4 min
Learn to fill arrays with for.
Filling arrays
You can fill an array with a for loop. The index goes from 0 to length - 1:
int[] arr = new int[5];
for (int i = 0; i < arr.length; i++) {
arr[i] = i * 2;
}
// arr = {0, 2, 4, 6, 8}Here each element becomes twice its index. The bound i < arr.length is safe; it never exceeds length. To print the array, use for-each.
Filling and printing
After filling the array, you can print it with for-each:
int[] arr = new int[5];
for (int i = 0; i < arr.length; i++) {
arr[i] = i * 2;
}
for (int n : arr) {
System.out.println(n);
}This prints 0, 2, 4, 6, 8. for-each walks the array without an index; it is ideal for printing. Filling needs an index, so the classic for is used.
Practice Fill with even numbers and print
Write a Main class with a main method. Assign new int[5] to int[] arr. With for (int i = 0; i < 5; i++) do arr[i] = i * 2. Then print all elements with for (int n : arr) { System.out.println(n); }.
Sample solution
public class Main {
public static void main(String[] args) {
int[] arr = new int[5];
for (int i = 0; i < 5; i++) {
arr[i] = i * 2;
}
for (int n : arr) {
System.out.println(n);
}
}
}Expected output
0 2 4 6 8
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What does for (int i = 0; i < arr.length; i++) arr[i] = i; do?
- Nothing
- Deletes the array
- Sorts the array
- Fills with 0, 1, 2, ... Correct answer
Explanation: Each element gets its index: 0, 1, 2, ...
2 Complete the fill loop
for (int i = 0; i < arr.length; i++) {
arr[i] = ____;
}for (int i = 0; i < arr.length; i++) {
arr[i] = i;
}Explanation: arr[i] = i writes the index value to each element.
3 Match the fill concepts
| Term | Meaning |
|---|---|
for |
Filling |
i < length |
Bound |
arr[i] = |
Assignment |
for-each |
Printing |