Assignment OperatorsS2C Home « Assignment Operators

Symbols used for mathematical and logical manipulation that are recognized by the compiler are commonly known as operators in Java. In the third of five lessons on operators we look at the assignment operators available in Java.

Assignment Operators Overview Top

The single equal sign = is used for assignment in Java and we have been using this throughout the lessons so far. This operator is fairly self explanatory and takes the form variable = expression; . A point to note here is that the type of variable must be compatible with the type of expression.

Shorthand Assignment Operators

The shorthand assignment operators allow us to write compact code that is implemented more efficiently.

Operator Meaning Example Result Notes
+=Additionint b = 5; b += 5;10
-=Subtractionint b = 5; b -= 5;0
/=Divisionint b = 7, b /= 22;3When used with an integer type, any remainder will be truncated.
*=Multiplicationint b = 5; b *= 5;25
%=Modulusint b = 5; b %= 2;1Holds the remainder value of a division.
&=ANDboolean a = false;
boolean b = false;
if (a &= b) {..}


boolean a = false;
boolean b = true;
if (a &= b) {..}


boolean a = true;
boolean b = false;
if (a &= b) {..}


boolean a = true;
boolean b = true;
if (a &= b) {..}


false



false



false



true
Will check both operands for true values and assign true or false to the first operand dependant upon the outcome of the expression.
|=ORboolean a = false;
boolean b = false;
if (a |= b) {..}


boolean a = false;
boolean b = true;
if (a |= b) {..}


boolean a = true;
boolean b = false;
if (a |= b) {..}


boolean a = true;
boolean b = true;
if (a |= b) {..}


false



true



true



true
Will check both operands for true values and assign true or false to the first operand dependant upon the outcome of the expression.
^=XORboolean a = false;
boolean b = false;
if (a ^= b) {..}


boolean a = false;
boolean b = true;
if (a ^= b) {..}


boolean a = true;
boolean b = false;
if (a ^= b) {..}


boolean a = true;
boolean b = true;
if (a ^= b) {..}


false



true



true



false
Will check both operands for different boolean values and assign true or false to the first operand dependant upon the outcome of the expression.

Automatic Type Conversion, Assignment Rules Top

The following table shows which types can be assigned to which other types, of course we can assign to the same type so these boxes are greyed out.

When using the table use a row for the left assignment and a column for the right assignment. So in the highlighted permutations byte = int won't convert and int = byte will convert.

Type boolean char byte short int long float double
boolean = NONONONONONONO
char = NONONONONONONO
byte = NONONONONONONO
short = NONOYESNONONONO
int = NOYESYESYESNONONO
long = NOYESYESYESYESNONO
float = NOYESYESYESYESYESNO
double = NOYESYESYESYESYESYES

Casting Incompatible Types Top

The above table isn't the end of the story though as Java allows us to cast incompatible types. A cast instructs the compiler to convert one type to another enforcing an explicit type conversion.

A cast takes the form    target = (target-type) expression.

There are a couple of things to consider when casting incompatible types:

  • With narrowing conversions such as an int to a short there may be a loss of precision if the range of the int exceeds the range of a short as the high order bits will be removed.
  • When casting a floating-point type to an integer type the fractional component is lost through truncation.
  • The target-type can be the same type as the target or a narrowing conversion type.
  • The boolean type is not only incompatible but also inconvertible with other types.

Lets look at some code to see how casting works and the affect it has on values:


package info.java8;
/*
  Casting Incompatible Types
*/ 
public class Casting {

  public static void main (String[] args) {
    char a = 'D';
    short b = 129;
    int c = 4127;
    long d = 33445566L;
    float e = 12.34F;
    double f = 456.789;
    byte g = (byte) a;
    System.out.println(a + " Cast char to byte: " + g); 
    g = (byte) b;
    System.out.println(b + " Cast short to byte: " + g); 
    g = (byte) c;
    System.out.println(c + " Cast int to byte: " + g); 
    g = (byte) d;
    System.out.println(d + " Cast long to byte: " + g); 
    g = (byte) e;
    System.out.println(e + " Cast float to byte: " + g); 
    g = (byte) f;
    System.out.println(e + " Cast double to byte: " + g); 
  }
}

Running the Casting class produces the following output:

run casting
Screenshot 1. Running the Casting class.

The first thing to note is we got a clean compile because of the casts, all the type conversions would fail otherwise. You might be suprised by some of the results shown in the screenshot above, for instance some of the values have become negative. Because we are truncating everything to a byte we are losing not only any fractional components and bits outside the range of a byte, but in some cases the signed bit as well. Casting can be very useful but just be aware of the implications to values when you enforce explicit type conversion.

Related Quiz

Fundamentals Quiz 8 - Assignment Operators Quiz

Lesson 9 Complete

In this lesson we looked at the assignment operators used in Java.

What's Next?

In the next lesson we look at the bitwise logical operators used in Java.