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Arithmetic Operators

The Java language supports various arithmetic operators for all floating-point and integer numbers. These include + (addition), - (subtraction), * (multiplication), / (division), and % (modulo). For example, you can use this Java code to add two numbers:

addThis + toThis

Or you can use the following Java code to compute the remainder that results from dividing divideThis by byThis:

divideThis % byThis

This table summarizes Java's binary arithmetic operations:

Operator	Use	Description
+	op1 + op2	Adds op1 and op2
-	op1 - op2	Subtracts op2 from op1
*	op1 * op2	Multiplies op1 by op2
/	op1 / op2	Divides op1 by op2
%	op1 % op2	Computes the remainder of dividing op1 by op2

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Note:  The Java programming language extends the definition of the + operator to include string concatenation. You'll see more about this in Strings.

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Here's an example program, ArithmeticDemo, that defines two integers and two double-precision floating point numbers and uses the five arithmetic operators to perform different arithmetic operations. This program also uses + to concatenate strings. The arithmetic operations are shown in red:

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

        //a few numbers
        int i = 37;
        int j = 42;
        double x = 27.475;
        double y = 7.22;

        //adding numbers
        System.out.println("Adding...");
        System.out.println("    i + j = " + (i + j));
        System.out.println("    x + y = " + (x + y));

        //subtracting numbers
        System.out.println("Subtracting...");
        System.out.println("    i - j = " + (i - j));
        System.out.println("    x - y = " + (x - y));

        //multiplying numbers
        System.out.println("Multiplying...");
        System.out.println("    i * j = " + (i * j));
        System.out.println("    x * y = " + (x * y));

        //dividing numbers
        System.out.println("Dividing...");
        System.out.println("    i / j = " + (i / j));
        System.out.println("    x / y = " + (x / y));

        //computing the remainder resulting from dividing numbers
        System.out.println("Computing the remainder...");
        System.out.println("    i % j = " + (i % j));
        System.out.println("    x % y = " + (x % y));

        //mixing types
        System.out.println("Mixing types...");
        System.out.println("    j + y = " + (j + y));
        System.out.println("    i * x = " + (i * x));
    }
}

The output from this program is:

Adding...
    i + j = 79
    x + y = 34.695
Subtracting...
    i - j = -5
    x - y = 20.255
Multiplying...
    i * j = 1554
    x * y = 198.37
Dividing...
    i / j = 0
    x / y = 3.8054
Computing the remainder...
    i % j = 37
    x % y = 5.815
Mixing types...
    j + y = 49.22
    i * x = 1016.58

Note that when an integer and a floating point number are used as operands to a single arithmetic operation, the result is floating point. The integer is implicitly converted to a floating point number before the operation takes place. The following table summarizes the data type returned by the arithmetic operators based on the data type of the operands. The necessary conversions take place before the operation is performed:

#include tables/conversions.mem4

In addition to the binary forms of + and -, each of these operatators have unary versions that perform the following operations:

Operator	Use	Description
+	+op	Promotes op to int if it's a byte, short, or char
-	-op	Arithmetically negates op

There also are two short cut arithmetic operators, ++ which increments its operand by 1, and -- which decrements its operand by 1. Either ++ or -- can appear before (prefix) or after (postfix) its operand. The prefix version, ++op/--op, evaluates to the value of the operand after the increment/decrement operation. The postfix version, op++/op--, evaluates the value of the operand before the increment/decrement operation.

Recall the SortDemo program.

public class SortDemo {
    public static void main(String[] args) {
        int[] arrayOfInts = { 32, 87, 3, 589, 12, 1076,
                              2000, 8, 622, 127 };

        for (int i = arrayOfInts.length; --i >= 0; ) {
            for (int j = 0; j < i; j++) {
                if (arrayOfInts[j] > arrayOfInts[j+1]) {
                    int temp = arrayOfInts[j];
                    arrayOfInts[j] = arrayOfInts[j+1];
                    arrayOfInts[j+1] = temp;
                }
            }
        }

        for (int i = 0; i < arrayOfInts.length; i++) {
            System.out.print(arrayOfInts[i] + " ");
        }
        System.out.println();
    }
}

Let's look at how the SortDemo program uses -- to control the outer of its two nested sorting loops. Here's the statement that controls the outer loop:

for (int i = arrayOfInts.length; --i >= 0; ) {
    ...
}

The return value of the operation --i is compared to 0 to determine whether to terminate the loop. Using the prefix version of -- means that the last iteration of this loop occurs when i is equal to 0. If we changed the code to use the postfix version of --, the last iteration of this loop occurs when i is equal to -1, which is incorrect for this program.

The other two loops in the program use the the postfix version of ++. In both cases, the version used doesn't really matter because the value returned by the operator isn't used for anything. When the return value of one of these shortcup operations isn't used for anything, convention prefers the postfix version.

The short cut increment/decrement operators are summarized in the following table:

Operator	Use	Description
++	op++	Increments op by 1; evaluates to the value of op before it was incremented
++	++op	Increments op by 1; evaluates to the value of op after it was incremented
--	op--	Decrements op by 1; evaluates to the value of op before it was decremented
--	--op	Decrements op by 1; evaluates to the value of op after it was decremented

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