initializing a boolean array in java

Question

I have this code

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

could someone tell me what exactly i'm doing wrong here and how would i correct it? I just need to initialize all the array elements to Boolean false. thank you

BalusC · Accepted Answer · 2013-01-02T16:17:51.277

310

I just need to initialize all the array elements to Boolean false.

Either use boolean[] instead so that all values defaults to false:

boolean[] array = new boolean[size];

Or use Arrays#fill() to fill the entire array with Boolean.FALSE:

Boolean[] array = new Boolean[size];
Arrays.fill(array, Boolean.FALSE);

Also note that the array index is zero based. The freq[Global.iParameter[2]] = false; line as you've there would cause ArrayIndexOutOfBoundsException. To learn more about arrays in Java, consult this basic Oracle tutorial.

edited Jan 02 '13 at 16:17

answered Mar 02 '10 at 16:42

BalusC

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The second piece of code is beneficial for the case when we wanna initialize it (set it) to all true values. Great answer! – despot Sep 06 '11 at 13:11
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I'd rather inverse the variable name and use the default initialization with false values. – BalusC Jul 03 '15 at 18:27
I am actually in favor of `Boolean[] array` as it allows you to have three states for each element: `true`, `false` and `null`, which is useful for cases where you want to note that something is "not processed". – Abhishek Divekar Jul 24 '19 at 08:29

score 21 · Answer 2 · edited Nov 20 '13 at 21:58

21

The array will be initialized to false when you allocate it.

All arrays in Java are initialized to the default value for the type. This means that arrays of ints are initialised to 0, arrays of booleans are initialised to false and arrays of reference types are initialised to null.

edited Nov 20 '13 at 21:58

Andrew Barber

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answered Mar 02 '10 at 16:41

Jørgen Fogh

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He's using `Boolean`, not `boolean`, so it will default to `null`. – BalusC Mar 02 '10 at 16:50
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Correct. I did not see that. Arrays.fill should do the trick. – Jørgen Fogh Mar 02 '10 at 17:15
Does this apply to all versions of Java? – Spyre Jan 04 '21 at 14:20
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@Spyre: Yes. This behavior is part of the definition of the language. – Jørgen Fogh Jan 09 '21 at 15:55

score 9 · Answer 3 · answered Mar 02 '10 at 16:43

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Arrays in Java start indexing at 0. So in your example you are referring to an element that is outside the array by one.

It should probably be something like freq[Global.iParameter[2]-1]=false;

You would need to loop through the array to initialize all of it, this line only initializes the last element.

Actually, I'm pretty sure that false is default for booleans in Java, so you might not need to initialize at all.

Best Regards

answered Mar 02 '10 at 16:43

Big Endian

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He's using `Boolean`, not `boolean`, so it will default to `null`. – BalusC Mar 02 '10 at 16:45

score 5 · Answer 4 · answered Mar 02 '10 at 16:42

5

They will be initialized to false by default. In Java arrays are created on heap and every element of the array is given a default value depending on its type. For boolean data type the default value is false.

answered Mar 02 '10 at 16:42

codaddict

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He's using `Boolean`, not `boolean`, so it will default to `null`. – BalusC Mar 02 '10 at 16:51
i meant to use boolean, my bad...sorry for the mislead – leba-lev Mar 02 '10 at 16:56

score 2 · Answer 5 · answered Mar 02 '10 at 16:42

2

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

Global.iParameter[2]:

It should be const value

answered Mar 02 '10 at 16:42

oneat

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this is not true. could be variables as well. the problem is that you are using Global.iParameter[2] to access the array. but the indices are going from 0 until only Global.iParameter[2]-1 !! – Karussell Mar 02 '10 at 16:47

score 0 · Answer 6 · answered Dec 03 '20 at 11:13

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The main difference is that Boolean is an object and boolean is an primitive.

Object default value is null;
boolean default value is false;

answered Dec 03 '20 at 11:13

Java bee

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initializing a boolean array in java

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