Java Number Operations

Java Number Operations

Most computer languages have both integers and floating point numbers. Java has the following primitive number types

• Each integer and float type is composed of one or more bytes of memory. For integers, the number of bytes of storage determines how large the number can be (its magnitude). For floating point numbers, the number of bytes of storage also determines the maximum scale of the number; in other words, how many decimal places of accuracy can be represented.

  As you can see, since float and double can only be represented to a certain number of decimal places, many floats and doubles will be slightly inaccurate. When this built-in inaccuracy could affect your calculations, you can instead use BigDecimal to represent a floating point number.

• Java Arithmetic

  Programming arithmetic in Java is no different from using a graphing calculator—or pencil and paper, for that matter.

  Examples:

 int result = 5 + 5;
 result = 5 - 5;
 result = 5 * 5; //multiplication
 result = 5 / 5;
 result = 5 % 5; //modulus division

Order of Precedence

The order of precedence of the arithmetic operators is identical to that of mathematics. As in algebra, the use of parentheses '()' can be used to change the default order of precedence. The following are usage examples for arithmetic-related operators, grouped by their order of precedence.

Highest precedence ++/-- postfix operators and parentheses '()':

 int a = 55;
 int c = a++; //c == 55, a == 56
 c = a--;     //c == 56, a == 55
 int d = (49 + 1) * 2 //the parentheses change the precedence

As you can see, the postfix operators return their value, then increment/decrement themselves.

Next highest precedence ++/-- prefix operators:

 int a = 55;
 int c = ++a; //c == 56, a == 56
 c = --a;     //c == 55, a == 55

The prefix operators, on the other hand, increment/decrement themselves first. Then, they return their new value.

Next highest precedence is the (type) cast operator:

 int a = (int)55.55f; //force a float into an int variable
 short c = (short)a;  //force an int into a short variable

Next highest precedence is the standard multiplicative operators, * / %.

 int a = 2 * 2; //a == 4
 int b = 2 / 2; //b == 1
 int c = 5 % 2; //c == 1

Next highest precedence is the standard additive operators, + -.

 int a = 2 + 2; //a == 4
 int b = 2 - 2; //b == 0

Last in order of precedence, we have the standard assignment operator '=' and the shortcut assignment operators '=op' where op is another operator such as * / % + -, etc. These shortcut operators allow you to apply an operator and assign the result in one step.

Examples:

 int result = 10;
 result += 10; //result == 20, the sum of result and 10
 result /= 5;  //result == 4, the quotient of result divided by 5

Numeric Type Conversions

When you assign a value to a variable of a different type (say, int to short or float to double), one of two things will happen. The value will be implicitly cast (converted) to the new type if it is a widening conversion. If it is a narrowing conversion, a compiler error will be thrown.

When going from an int and long value to a float or double, the value will be implicitly converted. If you want to go from a float or double to an int or long, however, you'll need to use an explicit cast. Be aware that this will truncate the decimal portion of the float or double.

Examples:

 //Widening conversions
 int a = 123123123;
 float b = a; //ok
 long c = a;  //ok

 //Narrowing conversions
 long a = 123123L
 int b = a;       //compiler error
 int c = (int)a;  //ok

 long d = 123123123123L
 int e = (int)d;  //loss of magnitude

Converting Between Numbers and Java Strings

• Very commonly, especially in web application, numbers need to be converted to Strings, and vice versa. An HTML form only deals with one data type—text. When the text is posted to a Java servlet, the servlet will often convert the text values to numbers for calculations or for persisting to a database.

• Java String to Number Conversion

  To convert a Java String to a number, you need to parse it using the appropriate primitive "wrapper" class, e.g. java.lang.Integer.

  Example:

 String s = "100";
 int i = java.lang.Integer.parseInt(s);

Number to Java String Conversion

There are several ways to convert from a number to a Java String. The first is to concatenate the number with an empty String using the '+' operator. The second is use the appropriate "wrapper" class's toString().

Examples:

 float price = 23.99f;
 String priceStr = "" + price;