What am I doing wrong when initializing a boolean array in Java, and how can I correctly set all elements to `false`?

General Discussions
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1

I’m trying to initialize a boolean array in Java like this:

public static Boolean freq[] = new Boolean[Global.iParameter[2]];
freq[Global.iParameter[2]] = false;

But I get an error. What exactly is causing the issue, and how can I properly initialize all elements of the array to Boolean.FALSE?

2

(I’ve been writing Java for over a decade, and initializing arrays can trip you up in sneaky ways.)

You’re actually pretty close with how you’re trying to initialize a boolean array java setup, but there are two common pitfalls you’ve hit:

:no_entry_sign: What’s going wrong?

public static Boolean freq[] = new Boolean[Global.iParameter[2]];
freq[Global.iParameter[2]] = false;

Here’s why this doesn’t work:

  • Index Out of Bounds: Arrays in Java are 0-indexed. So if your array size is n, the last valid index is n-1. Trying to access freq[n] will throw an ArrayIndexOutOfBoundsException.
  • Object vs Primitive: You’re using Boolean[] (object type) instead of boolean[] (primitive). Object arrays default to null, not false, which can cause NullPointerExceptions if accessed before being set.

:white_check_mark: Better Approach If all you need is true/false values and not nulls, use the primitive type. Java initializes all elements of a primitive boolean array java to false by default:

public static boolean[] freq = new boolean[Global.iParameter[2]];

You don’t have to manually set anything — the array is already filled with false values.

3

(I’ve run into this too, especially when working with object arrays for special logic like tri-state flags.)

@devan-skeem nailed the primitive side of things, but if you’re sticking with a Boolean[] for some reason — maybe because you need nulls for additional logic or optional flags — you’ll have to initialize the values yourself. Why? Because in a Boolean array java, the default values are null, not false.

Here’s a clean way to do it:

public static Boolean[] freq = new Boolean[Global.iParameter[2]];
for (int i = 0; i < freq.length; i++) {
    freq[i] = Boolean.FALSE;
}

It’s a bit more verbose, but it ensures every element is safely set to Boolean.FALSE. This helps avoid surprises when checking values later in your code.

4

(Been optimizing Java snippets for readability and performance — little tweaks add up over time!) Love how @prynka.chatterjee explained the manual loop! But if you’re looking for something a bit more elegant and concise — especially in a Boolean array java context — Java’s Arrays.fill() utility is your friend.

Here’s how you do it:

import java.util.Arrays;

public static Boolean[] freq = new Boolean[Global.iParameter[2]];
Arrays.fill(freq, Boolean.FALSE);

It’s cleaner, reduces boilerplate, and makes it crystal clear that you’re initializing the entire array with a consistent default value.