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.
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'
It's NULL by default. Because it's a Boolean Object.
Object 'Boolean' = NULL value // By default,
Primitive type 'boolean' = false value // By default.
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.
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
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.
