Is Java's default value for Boolean 'true'?

Question

Why does private Boolean shouldDropTables; assign true by default to the variable instead of NULL, like when writing private Integer anInteger;?

I am asking because I came across some code where there was an evaluation on a shouldDropTables Boolean variable being NULL or not determining whether to execute a method.

"Why does private Boolean shouldDropTables; assign true by default to the variable instead of NULL" It does not. Some other code is needed for that, which is not shown in this question. — Suma, Jul 03 '18 at 10:50
The answers here are good but there is no context and wrong assumptions. This question is not on topic for SO — EpicKip, Jul 03 '18 at 11:08

score 92 · Accepted Answer · edited Jul 05 '18 at 14:34

92

Boolean (with a uppercase 'B') is a Boolean object, which if not assigned a value, will default to null. boolean (with a lowercase 'b') is a boolean primitive, which if not assigned a value, will default to false.

Boolean objectBoolean;
boolean primitiveBoolean;

System.out.println(objectBoolean); // will print 'null'
System.out.println(primitiveBoolean); // will print 'false'

edited Jul 05 '18 at 14:34

geocodezip

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answered May 18 '11 at 17:00

nicholas.hauschild

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score 12 · Answer 2 · edited Jul 05 '18 at 14:25

12

No.

Boolean is null by default.

edited Jul 05 '18 at 14:25

TylerH

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answered May 18 '11 at 17:00

jmj

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score 5 · Answer 3 · edited Jul 04 '18 at 01:01

5

It's NULL by default. Because it's a Boolean Object.

Object 'Boolean' =  NULL value          // By default,
Primitive type 'boolean' = false value  // By default.

edited Jul 04 '18 at 01:01

Peter Mortensen

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answered May 18 '11 at 17:01

Saurabh Gokhale

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score 4 · Answer 4 · edited Nov 29 '18 at 11:24

4

I just wanted to add one point (for beginners) regarding a primitive boolean variable.

As @99tm answered, the default value is "false". This is correct for instance or class variables.

If you have a method local variable (i.e. local to a method) as a primitive boolean, there is no default value and it is not an Object so it also cannot be null.

You must initialize it before using it, otherwise it's a compilation error.

edited Nov 29 '18 at 11:24

Adam

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answered Feb 17 '14 at 15:57

sakura

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I never knew that about primitives. Now I'll have to look up what `int` and `double` are initialized to when instance variables. – Adam Nov 29 '18 at 11:25

score 3 · Answer 5 · answered May 18 '11 at 17:05

Perhaps you're not seeing some initialization.

It has null by default. See this sample:

$ cat B.java
class B {
        private Boolean shouldDrop;
        public static void main( String ... args ) {
                System.out.println( new B().shouldDrop );
        }
}

$ javac B.java

$ java B
null

I hope that helps

Roland · Answer 6 · 2017-09-25T15:27:18.680

2

JLS 9, 4.12.5. Initial Values of Variables

For type boolean, the default value is false.

For all reference types (§4.3), the default value is null.

Boolean is a reference type, therefore the default value is null.

edited Sep 25 '17 at 15:27

answered Sep 12 '17 at 07:45

Roland

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Is Java's default value for Boolean 'true'?

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