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.

Answer 2

Here is a short explanation with some examples.

Declaration: Declaration is when you declare a variable with a name, and a variable can be declared only once.

Example: int x;, String myName;, Boolean myCondition;

Initialization: Initialization is when we put a value in a variable, this happens while we declare a variable.

Example: int x = 7;, String myName = "Emi";, Boolean myCondition = false;

Assignment: Assignment is when we already declared or initialized a variable, and we are changing the value. You can change value of the variable as many time you want or you need.

Example:

int x = 7; x = 12; .......We just changed the value.

String myName = "Emi"; myName = "John" .......We just changed the value.

Boolean myCondition = false; myCondition = true; .......We just changed the value.

Note: In memory will be saved the last value that we put.

Answer 3

Declaration is not to declare "value" to a variable; it's to declare the type of the variable.

Assignment is simply the storing of a value to a variable.

Initialization is the assignment of a value to a variable at the time of declaration.

These definitions also applies to fields.

int i;  // simple declaration
i = 42  // simple assignment

int[] arr = { 1, 2, 3 };
// declaration with initialization, allows special shorthand syntax for arrays

arr = { 4, 5, 6 }; // doesn't compile, special initializer syntax invalid here
arr = new int[] { 4, 5, 6 }; // simple assignment, compiles fine

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However, it should be mentioned that "initialization" also has a more relaxed definition of "the first assignment to a variable", regardless of where it happens.

int i; // local variable declaration
if (something) i = 42;
System.out.println(i);
  // compile time error: The local variable i may not have been initialized

This, however, compiles:

int i; // the following also compiles if i were declared final
if (something) i = 42;
else i = 666;
System.out.println(i);

Here i can be "initialized" from two possible locations, by simple assignments. Because of that, if i was an array, you can't use the special array initializer shorthand syntax with this construct.

So basically "initialization" has two possible definitions, depending on context:

• In its narrowest form, it's when an assignment is comboed with declaration.
  • It allows, among other things, special array shorthand initializer syntax
• More generally, it's when an assignment is first made to a variable.
  • It allows, among other things, assignments to a final variable at multiple places.
    • The compiler would do its best to ensure that exactly one of those assignments can happen, thus "initializing" the final variable

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There's also JVM-context class and instance initialization, OOP-context object initialization, etc.

Answer 4

String declaration;
String initialization = "initialization";
declaration = "initialization"; //late initialization - will initialize the variable.
    // Without this, for example, in java, you will get a compile-time error if you try 
    // to use this variable.

declaration = "assignment"; // Normal assignment. 
    // Can be done any number of times for a non-final variable

Answer 5

declaration: whenever you define a new variable with its type

assignment: whenever you change the value of a variable by giving it a new value

initialization: an assignment that is done together with the declaration, or in any case the first assignment that is done with a variable, usually it's a constructor call for an object or a plain assignment for a variable

Answer 6

assignment: throwing away the old value of a variable and replacing it with a new one

initialization: it's a special kind of assignment: the first. Before initialization objects have null value and primitive types have default values such as 0 or false. Can be done in conjunction with declaration.

declaration: a declaration states the type of a variable, along with its name. A variable can be declared only once. It is used by the compiler to help programmers avoid mistakes such as assigning string values to integer variables. Before reading or assigning a variable, that variable must have been declared.