This concept says, boolean take the default value and does not required any pre-assignment if at class level
How ever if it is a local variable ie defined inside the method then compilation error for uninitialized variable might occur.
If we do like :
boolean var = false;
Then it reassign the same value in 2 steps and make is much more slower.
1. Assign default value (false) to variable.
2. Assign user defined value to variable.
For better performance and clean code leave assignment to JVM