As in mathematics, operators in Java are used to produce new values from operands. Choosing the right operator at the right time is important in order to write clear code in a fast way.
Code samples in this post were compiled with a JDK 6.
Assignment Operators
The most common assignment operator in Java is the = operator. This operator simply assign values to variables. Nevertheless, the = operator can be composed with other operators like +, -, *, /, >>, <<, & and | forming the compound operators: +=, -=, *=, /=, >>=, <<=, &= and |=.
int i = 0;
int j = 0;
i += 2; // Which is the same that i = i + 2;
j *= 10 + 4; // Which is the same that j = j * (10 + 4)
Relational Operators
Relational operators are often used on if tests and result in a boolean value (true or false). Java has six relational operators which are: >, >=, <, <=, ==, and !=. All of them can perform comparisons on integers, floating-points or characters. Only the last two (== and !=) are used to perform comaprisons on boolean values, or object reference variables.
char sex = 'f';
if(sex
Relational r1 = new Relational();
Relational r2 = new Relational();
if(r1 == r2) {} // false
r1 = r2; // now they hold the same reference
if(r1 == r2) {} // true
instanceof Operator
The instanceof operator verifies if an object is of a particular type. To evaluate the type of an object (on the left), the operator uses a IS-A test for a class or interface (on the right). The IS-A test returns true if the object inherits from the class or implements the interface used in the test. Otherwise, the result is false.
class A {}
class B extends A {}
public class InstanceOf {
public static void main(String... args) {
A a = new B();
B b;
if(a instanceof B) { // the IS-A test passes
b = (B)a; // we can then downcast
}
}
}
Arithmetic Operators
Beyond the basic arithmetic operators +, -, *, and /, there are three other operators also widely used which are:
- the Remainder operator (
%); - the String Concatenation operator (
+); - the Increment and Decrement operators (
++and--, respectively).
The remainder operator % returns the remainder of a division operation.
int x = 10;
int y = 4;
int rem = x % y; // which will be 2
Observation: in Java expressions are evaluated from left to right. The operators *, /, and % have higher priority then + and - operators. Parentheses can be used to change the evaluation order.
The operator + can act as addition operator or string concatenation operator, which depends on the operands. If there is a string among the operands, the + becomes a string concatenation operator. If the operands are numbers, the + will perform the addition.
int i = 5;
int j = 5;
System.out.println("String" + i); // will print String5
System.out.println("String" + (i + j)); // will print String10
// because the parentheses
Finally, the increment and decrement operators will increment or decrement variables by one. The operator can prefix or postfix the operand. When the prefix approach is used, the operator is placed before the variable, and the operation is performed before the variable is used. When the postfix approach is employed, the operator is placed after the variable, and the increment or decrement operation takes place after the variable is used.
public class IncrementDecrement {
public static void main(String... args) {
int i = 0;
if(++i == 1) {
System.out.println("++i is performed before the test");
}
System.out.println("i = " + i--); // output : i = 1
}
}
Conditional Operators
The ternary conditional operator will decide which value to assign or return after evaluating a boolean expression. Here is the structure of the conditional operator:
(boolean expression) ? value if true : value if false
The first value is assigned or returned if the result of the expression is true. Otherwise, the second value is used. The parentheses are optionals and it is possible to nest conditional operators.
public class ConditionalTest {
public static void main(String... args) {
int i = 4;
int j = 5;
String result = ++i == 4 ? "i=4" :
(i + j++ > 10) ? "i+j>10" : "i+j }
}
Logical Operators
Logical operators in Java basically evaluate an expression and return a boolean value.
Short-Circuit Logical Operators
Short-circuit operators evaluate boolean expressions and return boolean values. Short-circuit operators are represented as follow:
||short-circuit OR&&short-circuit AND
A short-circuit AND (&&) will evaluate the left side of an expression first. If the result is false, the operator will not waste time evaluating the right side and will return false. The right side will be evaluated only if the result of the left side is true. If the result of both sides is true, the hole expression is evaluated as true. If one of them results false, the expression is evaluated as false.
As the short-circuit AND, the short-circuit OR (||) will start evaluating the left side of the expression. Nevertheless, if the result is true the right side will not be analysed and the result of the whole expression will be true. The right side will be evaluated only if the result of the expression on left side is false. So, if there is one true, the global result is true. If both sides are false, the final result is false.
public class ShortCircuitLogicalOperator {
public static void main(String... args) {
if(check(9) && check(11)) {
System.out.println("First IF");
}
if(false || check(13)) {
System.out.println("Second IF");
}
}
private static boolean check(int value) {
if(value % 2 < 2) {
return true;
}
return false;
}
}
The output of the code above is:
First IF Second IF
Not Short-Circuit Logical Operators
Not short-circuit operators are represented as follows:
|non-short-circuit OR&non-short-circuit AND
As not short-circuit operators will evaluate logical expressions like the operators && and ||. On the other hand, not short-circuit operators will evaluated ALWAYS both sides of the expression. Non-short-circuit OR (|) will return false if both sides of the logical expression are false. It returns true if one side is true. Non-short-circuit AND (&) returns true only if both sides are evaluated as true. Otherwise, it returns false.
public class NotShortCircuitLogicalOperator {
public static void main(String... args) {
int i = 0;
if((i++ < 1 & ++i > 1) | i == 2) {
System.out.println("Little puzzle");
}
}
}
Boolean Invert Logical Operator
The unary boolean invert (!) operator evaluates only boolean expression and returns its opposite value. So, if the result is true, it gets false and vice-versa.
Exclusive-OR (XOR) Logical Operator
The exclusive-OR (^) operator also used with boolean expressions and it evaluates BOTH sides of an expression. For an exclusive-OR (^) expression be true, EXACTLY one operand must be true.
public class ExclusiveOR {
public static void main(String... args) {
byte size1 = -127;
byte size2 = 127;
if(checkSize(size1) ^ checkSize(size2)) {
System.out.println("There is a size that passes the" +
" check AND a size that does not match. ");
}
}
private static boolean checkSize(byte i) {
if(i < 127) {
return true;
}
return false;
}
}
Bitwise Operators
Bitwise operators are operators that evaluate the bit value of each operand. They are used in expressions with integer values. If the operand is smaller than int, the primitive value will be converted to an int.
Following a list with the bitwise operators in Java.
~unary bitwise complement&bitwise AND|bitwise OR^bitwise XOR- Shift operators: <<, >>, and >>>
The unary bitwise complement simply invert the bit value. The bitwise operators AND, OR and XOR evaluate bits using simple logic. The shift operator << shifts bits of to left putting zeros on the right side (low order position). The shift operator >> shifts bits to the right side saving the number sign. In other words, a negative number remains negative after the operation. Finally, the shift operator >>> move bits to right without saving the number sign. In this case, zeros are inserted as most significant bits (on the left). All the operators can be also used with the assignment (=) operator.
Bitwise operators are generally used to pack a lot of information into a single variable, like masks, flags, etc.
public class BitwiseOperators {
public static void main(String... args) {
short i = 127;
long j = 0;
byte k = 85; // binary: 0101 0101
int l = 99; // binary: 0000 0000 0000 0000 0000 0000 0110 0011
int m = -99; // binary: 1111 1111 1111 1111 1111 1111 1001 1101
System.out.println("~i = " + ~i);
System.out.println("i&j = " + (i&j));
System.out.println("i|j = " + (i|j));
System.out.println("i^j = " + (i^k));
j |= i;
System.out.println("j (after j |= i) = " + j);
System.out.println("m>>4 = " + (m>>4)); // binary: 1111 1111 1111 1111 1111 1111 1111 1001
System.out.println("m>>>12 = " + (m>>>12)); // binary: 0000 0000 0000 1111 1111 1111 1111 1111
}
}
The output of the code above will be:
~i = -128 i&j = 0 i|j = 127 i^j = 42 j (after j |= i) = 127 m>>4 = -7 m>>>2 = 1048575
Observation: Java uses two’s-complement mechanism to sign integral types. More on this here.
Diego's notes 