Is there any difference between these two statements?

Question

1. float ff = 1.2f;
2. Float fo = new Float(1.2f);
3. double fg = 3.2d;
4. Double fh = new Double(2.1d);

Can I use '=' between the (1) and (3) or between the (2) and (4)??

Answer 1

Yes, 2 creates an Object.

Answer 2

Yes. The first declares a variable of the primitive type float and initializes it to 1.2.

While the second declares a variable of the reference type Float, creates an object of type Float and then assigns a reference to the variable.

Answer 3

Yes.

1. Makes a plain old data type (AKA a primitive type) called "float."
2. Makes a Java Object called Float that holds that value that happens to be identical to (1)

Responding to the edit questions:

You will see

1. "possible loss of precision" message if you try ff = fg.
2. "incompatible types" if you try fo = fh.
3. fg = ff will work fine (the float fits in a double).
4. fh = fo will still give you an "incompatible types".

Answer 4

Yes, first one is a primitive type and second is a boxing class which wraps capabilities of primitive float type, we need second for example for use in the collections. Before you have had to deal a lot with type conversion (I think until Java 1.5) now the existence of wrappers classes takes those capabilities. More information. here

Answer 5

Yeah primitive types can't be NULL, Objects can. Also the Float object has a bunch of useful utility functions attached to it.

Answer 6

new Float(1.2f) creates a new Float object every time, consuming memory.

If you use factory method Float.valueOf(1.2f) JVM may reuse existing Float object instances for the same value. It could create a new object instance only if there isn't already a Float instance with the same value.

Usually you'll want to use Float.valueOf(1.2f) instead of new Float(1.2f).

Also note that primitives and objects work differently with equals operator ==.

float x1 = 1.2f;
float x2 = 1.2f;

x1 == x2  // true

Float f1 = new Float(1.2f);
Float f2 = new Float(1.2f);

f1 == f2 // false

Answer 7

In real applications I suggest you not use float or Float, its not very accurate and almost never the right solution, use double or Double instead.