Java: define terms initialization, declaration and assignment

Question

I find the defs circular, the subjects are defined by their verbs but the verbs are undefined! So how do you define them?

The Circular Definitions

Answer 1

I come from a C/C++ background, but the ideas should be the same.

Declaration - When a variable is declared, it is telling the compiler to set aside a piece of memory and associate a name (and a variable type) with it. In C/C++ it could look like this:

int x;

The compiler sees this and sets aside an address location for x and knows what methods it should use to perform operations on x (different variable types will use different access operations). This way, when the compiler runs into the line

x = 3 + 5;

It knows to put the integer value 8 (not the floating point value 8) into the memory location also known as 'x'.

Assignment - This is when you stuff a value into the previously declared variable. Assignment is associated with the 'equals sign'. In the previous example, the variable 'x' was assigned the value 8.

Initialization - This is when a variable is preset with a value. There is no guarantee that a variable will every be set to some default value during variable declaration (unless you explicitly make it so). It can be argued that initialization is the first assignment of a variable, but this isn't entirely true, as I will explain shortly. A typical initialization is a blend of the variable declaration with an assignment as follows:

int x = 6;

The distinction between initialization and assignment becomes more important when dealing with constants, such as this...

const int c = 15;

When dealing with constants, you only get to assign their value at the time of declaration/initialization. Otherwise, they can't be touched. This is because constants are often located in program memory vs data memory, and their actual assignment is occurring at compile time vs run time.