Java will initialize fields with known default values so any explicit initialization of those same defaults is redundant and results in a larger class file (approximately three additional bytecode instructions per field). Example:
public class C { boolean b = false; // examples of redundant initializers byte by = 0; short s = 0; char c = 0; int i = 0; long l = 0; float f = .0f; // all possible float literals doable d = 0d; // all possible double literals Object o = null; MyClass mca[] = null; int i1 = 0, ia1[] = null; class Nested { boolean b = false; } }