By Doug Lowe
An assignment statement in Java uses the assignment operator (=) to assign the result of an expression to a variable. In its simplest form, you code it like this:variable = expression;
For example:int a = (b * c) / 4;
A compound assignment operator is an operator that performs a calculation and an assignment at the same time. All Java binary arithmetic operators (that is, the ones that work on two operands) have equivalent compound assignment operators:
|+=||Addition and assignment|
|-=||Subtraction and assignment|
|*=||Multiplication and assignment|
|/=||Division and assignment|
|%=||Remainder and assignment|
For example, the statementa += 10;
is equivalent toa = a + 10;
Technically, an assignment is an expression, not a statement. Thus, a = 5 is an assignment expression, not an assignment statement. It becomes an assignment statement only when you add a semicolon to the end.
An assignment expression has a return value just as any other expression does; the return value is the value that’s assigned to the variable. For example, the return value of the expression a = 5 is 5. This allows you to create some interesting, but ill-advised, expressions by using assignment expressions in the middle of other expressions. For example:int a; int b; a = (b = 3) * 2; // a is 6, b is 3
Using assignment operators in the middle of an expression can make the expression harder to understand, so it’s not recommend that.
Java Assignment Operators
Assigning a value to a variable seems straightforward enough; you simply assign the stuff on the right side of the '= 'to the variable on the left. Below statement 1 assigning value 10 to variable x and statement 2 is creating String object called name and assigning value "Amit" to it.Statement 1: x =10; Statement 2: String name = new String ("Amit");
Assignment can be of various types. Let’s discuss each in detail.
The equal (=) sign is used for assigning a value to a variable. We can assign a primitive variable using a literal or the result of an expression.int x = 7; // literal assignment int y = x + 2; // assignment with an expression int z = x * y; // assignment with an expression with literal
Casting lets you convert primitive values from one type to another. We need to provide casting when we are trying to assign higher precision primitive to lower precision primitive for example If we try to assign int variable (which is in the range of byte variable) to byte variable then the compiler will throw an exception called "possible loss of precision". Eclipse IDE will suggest the solution as well as shown below. To avoid such problem we should use type casting which will instruct compiler for type conversion.byte v = (byte) a;
For cases where we try to assign smaller container variable to larger container variables we do not need of explicit casting. The compiler will take care of those type conversions. For example, we can assign byte variable or short variable to an int without any explicit casting.
Assigning Literal that is too large for a variable
When we try to assign a variable value which is too large (or out of range ) for a primitive variable then the compiler will throw exception “possible loss of precision” if we try to provide explicit cast then the compiler will accept it but narrowed down the value using two’s complement method. Let’s take an example of the byte which has 8-bit storage space and range -128 to 127. In below program we are trying to assign 129 literal value to byte primitive type which is out of range for byte so compiler converted it to -127 using two’s complement method. Refer link for two’s complement calculation (http://en.wikipedia.org/wiki/Two's_complement)
Java Code: Go to the editor
Reference variable assignment
We can assign newly created object to object reference variable as belowString s = new String(“Amit”); Employee e = New Employee();
First line will do following things,
- Makes a reference variable named s of type String
- Creates a new String object on the heap memory
- Assigns the newly created String object to the reference variables
You can also assign null to an object reference variable, which simply means the variable is not referring to any object. The below statement creates space for the Employee reference variable (the bit holder for a reference value) but doesn't create an actual Employee object.Employee a = null;
Compound Assignment Operators
Sometime we need to modify the same variable value and reassigned it to a same reference variable. Java allows you to combine assignment and addition operators using a shorthand operator. For example, the preceding statement can be written as:i +=8; //This is same as i = i+8;
The += is called the addition assignment operator. Other shorthand operators are shown below table
Below is the sample program explaining assignment operators:
Java Code: Go to the editor
- Assigning a value to can be straight forward or casting.
- If we assign the value which is out of range of variable type then 2’s complement is assigned.
- Java supports shortcut/compound assignment operator.
Java Code Editor: