Arrays in Java: Storing and Looping Through Many Values

So far, each variable has held a single value. But what if you need to store 30 students' marks, or a list of city names? You could make 30 variables… or you could use an array. An array stores many values of the same type in one place, under one name — and you reach each value by its position number. Arrays are your first real data structure, and they're everywhere.

What is an array?

Think of an array as a row of numbered boxes, all holding the same type of value. Here's one holding five test scores:

The single most important thing to burn into your memory: array positions (indexes) start at 0, not 1. So the first item is at index 0, and in an array of 5 items the last is at index 4. This trips up every beginner — expect it.

Creating an array

There are two common ways. If you already know the values, list them in curly braces:

int[] scores = {85, 90, 78, 92, 88};
String[] cities = {"Delhi", "Mumbai", "Pune"};

If you know the size but not the values yet, create an empty array with new:

int[] marks = new int[5];   // 5 slots, all default to 0

Reading and changing values

Use square brackets with the index to get or set a value:

int[] scores = {85, 90, 78, 92, 88};

System.out.println(scores[0]);   // 85 (the FIRST element)
System.out.println(scores[2]);   // 78

scores[1] = 95;                  // change index 1 from 90 to 95

The length of an array

Every array knows its own size via .length (note: no parentheses — it's not a method):

int[] scores = {85, 90, 78, 92, 88};
System.out.println(scores.length);   // 5

Looping through an array

This is where arrays and loops become best friends. To visit every element, loop from 0 up to length:

int[] scores = {85, 90, 78, 92, 88};

for (int i = 0; i < scores.length; i++) {
    System.out.println("Score " + i + ": " + scores[i]);
}

Notice the condition is i < scores.length (less-than, not less-than-or-equal). That's deliberate — it stops at the last valid index. Even cleaner is the for-each loop when you don't need the index:

for (int score : scores) {
    System.out.println(score);
}

A quick real example: finding the highest score

int[] scores = {85, 90, 78, 92, 88};
int highest = scores[0];

for (int score : scores) {
    if (score > highest) {
        highest = score;
    }
}
System.out.println("Highest: " + highest);   // Highest: 92

This little "start with the first, then compare each one" pattern is one you'll reuse endlessly.

That off-by-one ArrayIndexOutOfBoundsException caught me more times than I'd like to admit early on — almost always from writing <= instead of < in my loop. Now it's automatic: index starts at 0, last index is length minus 1. Say it a few times and it sticks.

Key takeaways

• An array stores many values of the same type under one name; access them by index.
• Indexes start at 0 — the last one is length - 1.
• Get the size with .length (no parentheses); loop with for or for-each.
• Going out of range throws ArrayIndexOutOfBoundsException — check your bounds.

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