Operators - Beginning Java 8 Fundamentals - page 99

Suppose that there are two int variables, num1 and num2 . The following assignment, num1 = num2 , assigns the
value 200 stored in num2 to num1 :
int num1 = 100; // num1 is 100
int num2 = 200; // num2 is 200
num1 = num2; // num1 is 200. num2 is 200
num2 = 500; // num2 is 500. num1 is still 200
When you say num1 = num2 , the value stored in num2 is copied to num1 , and both num1 and num2 maintain their
own copy of the same value 200 . Later on, when num2 = 500 is executed, the value of only num2 changes to 500 . But
the value of num1 remains the same: 200 . Now, suppose there are two reference variable, ref1 and ref2 , which refer to
two different objects of the same class. If you write
Object ref1 = new Object(); // An object
Object ref2 = new Object(); // An object
ref1 = ref2;
the effect of the expression ref1 = ref2 is that both reference variables, ref1 and ref2 , now refer to the same object
in memory: the object that was being referred to by ref2 . After this assignment, both reference variables, ref1 and
ref2 , are equally capable of manipulating the object. The changes made to the object in memory by reference variable
ref1 will be observed by ref2 also and vice versa. The chapter on classes and objects discusses more about reference
variable assignments.
Declaration, Initialization, and Assignment
Before a variable of any type is used in a Java program, it must be declared and must have a value assigned to it.
Suppose you want to use an int variable named num1 . First, you must declare it.
int num1; // Declaration of a variable num1
A value can be assigned to a variable after it is declared or at the time of declaration itself. When a value is
assigned to a variable after it has been declared, it is known as assignment. The following piece of code declares an
int variable num2 and assigns 50 to it:
int num2; // Declaration of a variable num2
num2 = 50; // Assignment
When a value is assigned to a variable at the time of declaration itself, it is known as initialization. The following
code declares an int variable num3 and initializes it to a value 100:
int num3 = 100; // Declaration of variable num3 and its initialization
You can declare more than one variable of the same type in one declaration by separating each variable name by
a comma.
// Declaration of three variables num1, num2 and num3 of type int
int num1, num2, num3;