Core Java:Operators

Operators

Now that you've learned how to declare and initialize variables, you probably want to know how to do something with them. Learning the operators of the Java programming language is a good place to start. Operators are special symbols that perform specific operations on one, two, or three operands, and then return a result. As we explore the operators of the Java programming language, it may be helpful for you to know ahead of time which operators have the highest precedence. The operators in the following table are listed according to precedence order. The closer to the top of the table an operator appears, the higher its precedence. Operators with higher precedence are evaluated before operators with relatively lower precedence. Operators on the same line have equal precedence. When operators of equal precedence appear in the same expression, a rule must govern which is evaluated first. All binary operators except for the assignment operators are evaluated from left to right; assignment operators are evaluated right to left.

Operator Precedence

Operators	Precedence
postfix	expr++ expr--
unary	++expr --expr +expr -expr ~ !
multiplicative	* / %
additive	+ -
shift	<< >> >>>
relational	< > <= >= instanceof
equality	== !=
bitwise AND	&
bitwise exclusive OR	^
bitwise inclusive OR	|
logical AND	&&
logical OR	||
ternary	? :
assignment	= += -= *= /= %= &= ^= |= <<= >>= >>>=

In general-purpose programming, certain operators tend to appear more frequently than others; for example, the assignment operator "=" is far more common than the unsigned right shift operator ">>>". With that in mind, the following discussion focuses first on the operators that you're most likely to use on a regular basis, and ends focusing on those that are less common. Each discussion is accompanied by sample code that you can compile and run. Studying its output will help reinforce what you've just learned.

Assignment, Arithmetic, and Unary Operators

The Simple Assignment Operator One of the most common operators that you'll encounter is the simple assignment operator "=". You saw this operator in the Bicycle class; it assigns the value on its right to the operand on its left:

 int cadence = 0;
 int speed = 0;
 int gear = 1;

This operator can also be used on objects to assign object references, as discussed in Creating Objects.
The Arithmetic Operators
The Java programming language provides operators that perform addition, subtraction, multiplication, and division. There's a good chance you'll recognize them by their counterparts in basic mathematics. The only symbol that might look new to you is "%", which divides one operand by another and returns the remainder as its result.

+  additive operator (also used for String concatenation)
-  subtraction operator
* multiplication operator
/  division operator
% remainder operator

The following program, ArithmeticDemo, tests the arithmetic operators.

class ArithmeticDemo {

     public static void main (String[] args){
          
          int result = 1 + 2; // result is now 3
          System.out.println(result);

          result = result - 1; // result is now 2
          System.out.println(result);

          result = result * 2; // result is now 4
          System.out.println(result);

          result = result / 2; // result is now 2
          System.out.println(result);

          result = result + 8; // result is now 10
          result = result % 7; // result is now 3
          System.out.println(result);

     }
}

You can also combine the arithmetic operators with the simple assignment operator to create compound assignments. For example, x+=1; and x=x+1; both increment the value of x by 1. The + operator can also be used for concatenating (joining) two strings together, as shown in the following ConcatDemo program:

class ConcatDemo {
     public static void main(String[] args){
          String firstString = "This is";
          String secondString = " a concatenated string.";
          String thirdString = firstString+secondString;
          System.out.println(thirdString);
     }
}

By the end of this program, the variable thirdString contains "This is a concatenated string.", which gets printed to standard output. The Unary Operators
The unary operators require only one operand; they perform various operations such as incrementing/decrementing a value by one, negating an expression, or inverting the value of a boolean.

+  Unary plus operator; indicates positive value (numbers are positive without this, however)
-  Unary minus operator; negates an expression
++   Increment operator; increments a value by 1
--     Decrement operator; decrements a value by 1
!      Logical complement operator; inverts the value of a boolean

The following program, UnaryDemo, tests the unary operators:

class UnaryDemo {

     public static void main(String[] args){
          int result = +1; // result is now 1
          System.out.println(result);
          result--;  // result is now 0
          System.out.println(result);
          result++; // result is now 1 
          System.out.println(result);
          result = -result; // result is now -1
          System.out.println(result);
          boolean success = false;
          System.out.println(success); // false
          System.out.println(!success); // true
     }
}

The increment/decrement operators can be applied before (prefix) or after (postfix) the operand. The code result++; and ++result; will both end in result being incremented by one. The only difference is that the prefix version (++result) evaluates to the incremented value, whereas the postfix version (result++) evaluates to the original value. If you are just performing a simple increment/decrement, it doesn't really matter which version you choose. But if you use this operator in part of a larger expression, the one that you choose may make a significant difference. The following program, PrePostDemo, illustrates the prefix/postfix unary increment operator:

class PrePostDemo {
     public static void main(String[] args){
          int i = 3;
   i++;
   System.out.println(i); // "4"
   ++i;      
   System.out.println(i); // "5"
   System.out.println(++i); // "6"
   System.out.println(i++); // "6"
   System.out.println(i); // "7"
     }

}

Equality, Relational, and Conditional Operators

The Equality and Relational Operators The equality and relational operators determine if one operand is greater than, less than, equal to, or not equal to another operand. The majority of these operators will probably look familiar to you as well. Keep in mind that you must use "==", not "=", when testing if two primitive values are equal.

== equal to
!= not equal to
> greater than
>= greater than or equal to
< less than
<= less than or equal to

The following program, ComparisonDemo, tests the comparison operators:

class ComparisonDemo {

     public static void main(String[] args){
          int value1 = 1;
          int value2 = 2;
          if(value1 == value2) System.out.println("value1 == value2");
          if(value1 != value2) System.out.println("value1 != value2");
          if(value1 > value2) System.out.println("value1 > value2");
          if(value1 < value2) System.out.println("value1 < value2");
          if(value1 <= value2) System.out.println("value1 <= value2");
     }
}

Output:

value1 != value2
value1 < value2
value1 <= value2

The Conditional Operators
The && and || operators perform Conditional-AND and Conditional-OR operations on two boolean expressions. These operators exhibit "short-circuiting" behavior, which means that the second operand is evaluated only if needed.

&& Conditional-AND
|| Conditional-OR

The following program, ConditionalDemo1, tests these operators:

class ConditionalDemo1 {

     public static void main(String[] args){
          int value1 = 1;
          int value2 = 2;
          if((value1 == 1) && (value2 == 2)) System.out.println("value1 is 1 AND value2 is 2");
          if((value1 == 1) || (value2 == 1)) System.out.println("value1 is 1 OR value2 is 1");

     }
}

Another conditional operator is ?:, which can be thought of as shorthand for an if-then-else statement (discussed in the Control Flow Statements section of this lesson). This operator is also known as the ternary operator because it uses three operands. In the following example, this operator should be read as: "If someCondition is true, assign the value of value1 to result. Otherwise, assign the value of value2 to result."
The following program, ConditionalDemo2, tests the ?: operator:

class ConditionalDemo2 {

     public static void main(String[] args){
          int value1 = 1;
          int value2 = 2;
          int result;
          boolean someCondition = true;
          result = someCondition ? value1 : value2;

          System.out.println(result);

     }
}

Because someCondition is true, this program prints "1" to the screen. Use the ?: operator instead of an if-then-else statement if it makes your code more readable; for example, when the expressions are compact and without side-effects (such as assignments).
The Type Comparison Operator instanceof
The instanceof operator compares an object to a specified type. You can use it to test if an object is an instance of a class, an instance of a subclass, or an instance of a class that implements a particular interface.
The following program, InstanceofDemo, defines a parent class (named Parent), a simple interface (named MyInterface), and a child class (named Child) that inherits from the parent and implements the interface.

class InstanceofDemo {
  public static void main(String[] args) {

    Parent obj1 = new Parent();
    Parent obj2 = new Child();

    System.out.println("obj1 instanceof Parent: " + (obj1 instanceof Parent));
    System.out.println("obj1 instanceof Child: " + (obj1 instanceof Child));
    System.out.println("obj1 instanceof MyInterface: " + (obj1 instanceof MyInterface));
    System.out.println("obj2 instanceof Parent: " + (obj2 instanceof Parent));
    System.out.println("obj2 instanceof Child: " + (obj2 instanceof Child));
    System.out.println("obj2 instanceof MyInterface: " + (obj2 instanceof MyInterface));
  }
}

class Parent{}
class Child extends Parent implements MyInterface{}
interface MyInterface{}

Output:

obj1 instanceof Parent: true
obj1 instanceof Child: false
obj1 instanceof MyInterface: false
obj2 instanceof Parent: true
obj2 instanceof Child: true
obj2 instanceof MyInterface: true

When using the instanceof operator, keep in mind that null is not an instance of anything.