The best programs are written so that computing machines can perform them quickly and so that human beings can understand them clearly. A programmer is ideally an essayist who works with traditional aesthetic and literary forms as
well as mathematical concepts, to communicate the way that an algorithm works and to convince a reader that the results will be correct. Donald E. Knuth

Java Operators

Operators are used to perform mathematical & logical operations. Operators supported by Java can be categorized into arithmetic, logical, relational, bitwise (used for bit manipulation) and some special operators. Let's see how these operators are used in programming.

Arithmetic Operators
Arithmetic Operators supported by Java are ADD ( + ), SUBTRACT ( - ), MULTIPLY ( * ), DIVIDE ( / ),
MODULO ( % ), INCREMENT ( ++ ) and DECREMENT ( -- )
.
' / ' operator prints the quotient of the division operation and ' % ' operator prints the remainder of the division operation. For e.g, 5 / 2 = 2 and 5 % 2 = 1.
' ++ ' operator increments a value by 1 and ' -- ' operator decrements a value by 1. For e.g 5++ = 6 and 5-- = 4.
The behaviour of ' + ', ' - ' and ' * ' are trivial.
Let's look at the following program to see arithmetic operators in action :

/*
 * This program demonstrates the use of arithmetic operators
 */
public class Arithmetic {
    public static void main(String args[]) {
      int a = 5, b = 2;
      int x, y, z, r, s, u, v;
      x = a + b; // addition ( Value of a+b is assigned to x )
      y = a - b; // subtraction
      z = a * b; // multiplication
      r = a / b; // division
      s = a % b; // modulo
      System.out.println(" Sum of " + a + " and " + b + " is " + x);
      System.out.println(" Difference of " + a + " and "+ b + " is " + y);
      System.out.println(" Product of " + a + " and "+ b + " is " + z);
      System.out.println(" Division of " + a + " by "+ b + " is " + r);
      System.out.println(" Modulo of " + a + " by "+ b + " is " + s);
      System.out.println(" Incrementing a " + (++a));
      System.out.println(" Decrementing b " + (--b));
    }
}

Please note that some of the expressions in which a variable is present in both sides can be written as :

Expressionis Equivalent to
X = X + YX += Y
X = X - YX -= Y
X = X * YX *= Y
X = X / YX /= Y
X = X % YX %= Y

Logical Operators
Logical Operators supported by Java are AND ( && ), OR ( || ) and NOT ( ! ).
Consider two operands A and B.
A && B evaluates to True only if both A and B are True.
A || B evaluates to True if any of the two operands is True.
' ! ' operator negates the state of an operand. For e.g, if A = True, then !A = False.
Note that any non-zero value is considered True and zero is considered False.
Following program shows logical operators in action :

/*
 * This program demonstrates the use of logical operators
 */
public class Logical {
    public static void main(String args[]) {
	boolean a = true, b = false;
        boolean x, y, z;
        x = a && b;    // x = false
        y = a || b;    // y = true
        z = !b;        // z = true
        System.out.println(a + " AND " + b + " = " + x);
        System.out.println(a + " OR " + b + " = " + y);
        System.out.println("NOT " + b + " = " + z);
    }
}


Relational Operators
Relational operators ( used for comparison operations ) supported by Java are EQUAL ( == ),
NOT EQUAL ( != ), GREATER THAN ( > ), LESS THAN ( < ), GREATER THAN OR EQUAL TO ( >= ) and LESS THAN OR EQUAL TO ( <= )
.
Following program illustrates the behaviour of relational operators :

/*
 * This program demonstrates the use of relational operators
 */
public class Relational {
    public static void main(String args[]) {
      int a = 5, b = 2, c = 2;
      boolean x, y, z, r;
      x = ( b == c );   // x = 1 (true) since b is equal to c
      y = ( a != b );   // y = 1 (true) since a is not equal to b
      z = ( b < c );       // z = 0 (false) since b is not less than c
      r = ( b <= c );   // r = 1 (true) since b is not less but equal to c
      System.out.println(" x : "+ x);
      System.out.println(" y : "+ y);
      System.out.println(" z : "+ z);
      System.out.println(" r : "+ r);
    }
}


Bitwise Operators
Bitwise Operators ( used for bit manipulation ) supported by Java are BITWISE AND ( & ), BITWISE OR ( | ), BITWISE XOR ( ^ ), BITWISE NOT ( ~ ), LEFT SHIFT ( << ), RIGHT SHIFT ( >> ) and RIGHT SHIFT WITH ZERO FILL ( >>> ). These operators operate at bit level.
Consider two bits bit1 and bit2.
bit1 & bit2 evaluates to True if and only if both bit1 and bit2 are True.
bit1 | bit2 evaluates to True if any of the two bits is True.
bit1 ^ bit2 evaluates to True if and only if one of the bits is True.
~ operator toggles a bit. If bit1 = True, the ~bit1 = False.
' A << 2 ' left shifts the bits of a number (A) by 2 positions.
' A >> 1 ' right shifts the bits of a number (A) by 1 position.
' A >>> 1 ' right shifts the bits of a number (A) by 1 position and shifted values are filled up with zeroes.

Difference between >> and >>> operators
There is no difference between the two operators when we are dealing with positive integers. The difference is observed in case of negative integers. The Most Significant Bit ( MSB ) or the leftmost bit is 1 in case of negative integers ( i.e MSB is the sign bit ). Now, when we use >> on a negative integer, the sign bit is not shifted but if we use >>> operator, the sign bit is also shifted along with other bits and the position of sign bit is filled with 0 along with other shifted values.

Suppose A = 7 and B = 19. In binary format : A = 00000111 and B = 00010011
Following table shows how bitwise operators do bit manipulation :

Binary
A00000111
B00010011
A & B00000011
A | B00010111
A ^ B00010100
~A11111000
A << 200011100
A >> 100000011

Following program demonstrate the behaviour of bitwise operators :

/*
 * This program demonstrates the use of bitwise operators
 */
public class Bitwise {
    public static void main(String args[]) {
      int a = 7, b = 19, c = -7;
      int x, y, z, r, s, t, p, q;
      x = a & b;     /* 7 & 19 = (00000111 & 00010011) = 00000011 = 3  */
      y = a | b;     /* 7 | 19 = (00000111 | 00010011) = 00010111 = 23 */
      z = a ^ b;     /* 7 ^ 19 = (00000111 ^ 00010011) = 00010100 = 20 */
      r = a << 2;    /* 7 << 2 = (00000111 << 2) = 00011100 = 28 */
      s = a >> 1;    /* 7 >> 1 = (00000111 >> 1) = 00000011 = 3  */
      p = c >> 2;
      q = c >>> 2;
      System.out.println(a + " & " + b + " = " + x);
      System.out.println(a + " | " + b + " = " + y);
      System.out.println(a + " ^ " + b + " = " + z);
      System.out.println(a + " << " + 2 + " = " + r);
      System.out.println(a + " >> " + 1 + " = " + s);
      System.out.println(c + " >> " + 2 + " = " + p);
      System.out.println(c + " >>> " + 2 + " = " + q);
    }
}

Note that in the above program, there is no demonstration of NOT ( ~ ) operator since the result would be unexpected and will confuse you. You might have noticed that all decimal numbers are represented using 8 bits
( 1 Octet ) but in the system memory it is stored as a sequence of multiple octets (4 in case of 32 bit systems). In our case, other 3 octets would be all 0s. But NOT operation would toggle all those 0s to 1s which would result into a very high value ( outside the range of int ). As a result, some unexpected value would be displayed.

Special Operators

instanceofThis operator is applicable to objects only. It checks whether an object is of particular class type.
ConditionConditional Operator returns a value depending on a condition.
Syntax : ( Condition ? a : b ). If condition is true, a is returned else b is returned.
AssignmentIt is used to assign one value to other in an expression.
In the expression c = a + b, value of ( a + b ) is assigned to c.

Following program illustrates the use of conditional operator :

/*
 * This program demonstrates the use of conditional operator
 */
public class Conditional {
    public static void main(String args[]) {
      int a = 5, b = 2;
      /* if a > b, then value in 'a' assigned to 'c'
         else value in 'b' is assigned to 'a' */
      int c = ( a > b ) ? a : b; // c holds greater of a and b
      System.out.println("Greater of " + a + " and " + b + " is " + c);
    }
}

Following program illustrates the use instanceof operator :

/*
 * This program demonstrates the use of instanceOf operator
 */
public class Instance {
    public static void main(String args[]) {
      Instance inst = new Instance(); //create an object of Instance type
      String str = new String("abc"); //create an object/variable of String type
      boolean result1 = inst instanceof Instance; // result1 = true
      boolean result2 = str instanceof String;    // result2 = true
      System.out.println("result1 : " + result1);
      System.out.println("result2 : " + result2);
    }
}

The instanceof operator is not used much and the above program doesn't reflect a practical use case. It can be useful in knowing the actual class of an object when we are using inheritance, a feature which we will discuss later in the tutorial.

Operator Precedence & Associativity
Precedence of operators determines the order of evaluation of expression consisting of multiple operators.
Higher precedence operators will be evaluated first. Associativity determines whether an expression is evaluated left to right or right to left. Consider the expressions below :

x = 2 + 3 * 2 => x = 2 + 6 => x = 8 ( '*' has higher precedence than '+' )
y = 2 * 3 / 2 => y = 6 / 2 => y = 3 ( '*' and '/' has same precedence but associativity is left to right )
z = 3 / 2 * 2 => z = 1 * 2 => z = 2 ( '*' and '/' has same precedence but associativity is left to right )

Following table shows the precedence and associativity of the C++ operators ( Operator precedence decreases as we move downwards ) :

OperatorsPrecedence
Postfix ( ++, -- )Left to Right
Unary ( +, -, !, ~), Prefix ( ++, -- )Right to Left
*, /, %Left to Right
Additive ( +, - )Left to Right
Left and Right Shift ( <<, >>, >>> )Left to Right
Relational ( <, <=, >, >= )Left to Right
Equality ( ==, != )Left to Right
Bitwise AND ( & )Left to Right
Bitwise XOR ( ^ )Left to Right
Bitwise OR ( | )Left to Right
Logical AND ( && )Left to Right
Logical OR ( || )Left to Right
Conditional ( Condition ? x : y )Right to Left
Assignment ( = )Right to Left

*Note : Unary operators have single operand

Postfix and Prefix Operators
The increment (++) and decrement (--) operators can appear either on left side (prefix) or right side (postfix) of the operand. Following program demonstrates the behaviour of postfix and prefix operators :

/*
 * This program demonstrates the use of postfix and prefix operator
 */
public class PostfixPrefix {
    public static void main(String args[]) {
      int a = 5, b = 2;
      int c = 7, d = 3;
      int x, y, r, s;
      x = ++a;    // first increment a, then assign its value to x
      System.out.println(" x : " + x + ", a : " + a); // displays x : 6, a : 6
      y = b++;    // first assign value of b to y, then increment b
      System.out.println(" y : " + y + ", b : " + b); // displays y : 2, b : 3
      r = --c;    // first decrement c, then assign its value to r
      s = d--;    // first assign value of d to s, then decrement d
      System.out.println(" r : " + r + ", c : " + c); // displays r : 6, c : 6
      System.out.println(" s : " + s + ", d : " + d); // displays s : 3, c : 2
    }
}


Typecasting
Sometimes it is required to explicitly convert a variable from one data type to another. This concept is known as typecasting. Following program will make it clear.

/*
 * This program demonstrates typecasting
 */
public class Typecast {
    public static void main(String args[]) {
      int a = 7, b = 3;
      float x, y, z;
      x = a / b;          /* x = 2.0 */
      y = (float)a / b;   /* variable 'a' is typecasted [ y = 2.333333 ] */
      z = (float)(a / b); /* (a / b) is typecasted [ z = 2.0 ] */
      System.out.println("x = " + x + "\ny = " + y + "\nz = " + z);
    }
}

In the above program, both a and b are integers. Now, ( a / b ) = ( 7 / 3 )= 2 . Now, since x is a float type variable, so x stores 2.000000 . In case of y , variable a is converted to float and thus the expression is evaluated as
y = (float)a / b = ( 7.000000 / 3 ) = 2.333333. In case of z, the value of ( a / b ) is converted to float and the expression is evaluated as y = (float) ( a / b ) = float ( 7 / 3 ) = float ( 2 ) = 2.000000.

Automatic Type Conversion
In Java, we can mix variables and constants of different data types in an expression. During evaluation, operands of lower type is automatically converted to higher type. For e.g, If an expression consists of byte, int and float operands, the result is always promoted to float.

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