If the radix is smaller than or larger than , then the radix is used instead.
If the first argument is negative, the first element of the result is the ASCII minus sign (). If the first argument is not negative, no sign character appears in the result.
The remaining characters of the result represent the magnitude of the first argument. If the magnitude is zero, it is represented by a single zero character (); otherwise, the first character of the representation of the magnitude will not be the zero character. The following ASCII characters are used as digits:These are through and through . If is , then the first of these characters are used as radix- digits in the order shown. Thus, the digits for hexadecimal (radix 16) are . If uppercase letters are desired, the method may be called on the result:
- - a to be converted to a string.
- - the radix to use in the string representation.
- a string representation of the argument in the specified radix.
- See Also:
The Java programming language is statically-typed, which means that all variables must first be declared before they can be used. This involves stating the variable's type and name, as you've already seen:
Doing so tells your program that a field named "gear" exists, holds numerical data, and has an initial value of "1". A variable's data type determines the values it may contain, plus the operations that may be performed on it. In addition to , the Java programming language supports seven other primitive data types. A primitive type is predefined by the language and is named by a reserved keyword. Primitive values do not share state with other primitive values. The eight primitive data types supported by the Java programming language are:
byte: The data type is an 8-bit signed two's complement integer. It has a minimum value of -128 and a maximum value of 127 (inclusive). The data type can be useful for saving memory in large arrays, where the memory savings actually matters. They can also be used in place of where their limits help to clarify your code; the fact that a variable's range is limited can serve as a form of documentation.
short: The data type is a 16-bit signed two's complement integer. It has a minimum value of -32,768 and a maximum value of 32,767 (inclusive). As with , the same guidelines apply: you can use a to save memory in large arrays, in situations where the memory savings actually matters.
int: By default, the data type is a 32-bit signed two's complement integer, which has a minimum value of -231 and a maximum value of 231-1. In Java SE 8 and later, you can use the data type to represent an unsigned 32-bit integer, which has a minimum value of 0 and a maximum value of 232-1. Use the Integer class to use data type as an unsigned integer. See the section The Number Classes for more information. Static methods like , etc have been added to the class to support the arithmetic operations for unsigned integers.
long: The data type is a 64-bit two's complement integer. The signed long has a minimum value of -263 and a maximum value of 263-1. In Java SE 8 and later, you can use the data type to represent an unsigned 64-bit long, which has a minimum value of 0 and a maximum value of 264-1. Use this data type when you need a range of values wider than those provided by . The class also contains methods like , etc to support arithmetic operations for unsigned long.
float: The data type is a single-precision 32-bit IEEE 754 floating point. Its range of values is beyond the scope of this discussion, but is specified in the Floating-Point Types, Formats, and Values section of the Java Language Specification. As with the recommendations for and , use a (instead of ) if you need to save memory in large arrays of floating point numbers. This data type should never be used for precise values, such as currency. For that, you will need to use the java.math.BigDecimal class instead. Numbers and Strings covers and other useful classes provided by the Java platform.
double: The data type is a double-precision 64-bit IEEE 754 floating point. Its range of values is beyond the scope of this discussion, but is specified in the Floating-Point Types, Formats, and Values section of the Java Language Specification. For decimal values, this data type is generally the default choice. As mentioned above, this data type should never be used for precise values, such as currency.
boolean: The data type has only two possible values: and . Use this data type for simple flags that track true/false conditions. This data type represents one bit of information, but its "size" isn't something that's precisely defined.
char: The data type is a single 16-bit Unicode character. It has a minimum value of (or 0) and a maximum value of (or 65,535 inclusive).
In addition to the eight primitive data types listed above, the Java programming language also provides special support for character strings via the java.lang.String class. Enclosing your character string within double quotes will automatically create a new object; for example, . objects are immutable, which means that once created, their values cannot be changed. The class is not technically a primitive data type, but considering the special support given to it by the language, you'll probably tend to think of it as such. You'll learn more about the class in Simple Data Objects
It's not always necessary to assign a value when a field is declared. Fields that are declared but not initialized will be set to a reasonable default by the compiler. Generally speaking, this default will be zero or , depending on the data type. Relying on such default values, however, is generally considered bad programming style.
The following chart summarizes the default values for the above data types.
|Data Type||Default Value (for fields)|
|String (or any object)||null|
Local variables are slightly different; the compiler never assigns a default value to an uninitialized local variable. If you cannot initialize your local variable where it is declared, make sure to assign it a value before you attempt to use it. Accessing an uninitialized local variable will result in a compile-time error.
You may have noticed that the keyword isn't used when initializing a variable of a primitive type. Primitive types are special data types built into the language; they are not objects created from a class. A literal is the source code representation of a fixed value; literals are represented directly in your code without requiring computation. As shown below, it's possible to assign a literal to a variable of a primitive type:
An integer literal is of type if it ends with the letter or ; otherwise it is of type . It is recommended that you use the upper case letter because the lower case letter is hard to distinguish from the digit .
Values of the integral types , , , and can be created from literals. Values of type that exceed the range of can be created from literals. Integer literals can be expressed by these number systems:
- Decimal: Base 10, whose digits consists of the numbers 0 through 9; this is the number system you use every day
- Hexadecimal: Base 16, whose digits consist of the numbers 0 through 9 and the letters A through F
- Binary: Base 2, whose digits consists of the numbers 0 and 1 (you can create binary literals in Java SE 7 and later)
For general-purpose programming, the decimal system is likely to be the only number system you'll ever use. However, if you need to use another number system, the following example shows the correct syntax. The prefix indicates hexadecimal and indicates binary:
A floating-point literal is of type if it ends with the letter or ; otherwise its type is and it can optionally end with the letter or .
The floating point types ( and ) can also be expressed using E or e (for scientific notation), F or f (32-bit float literal) and D or d (64-bit double literal; this is the default and by convention is omitted).
Character and String Literals
Literals of types and may contain any Unicode (UTF-16) characters. If your editor and file system allow it, you can use such characters directly in your code. If not, you can use a "Unicode escape" such as (capital C with circumflex), or (Sí Señor in Spanish). Always use 'single quotes' for literals and "double quotes" for literals. Unicode escape sequences may be used elsewhere in a program (such as in field names, for example), not just in or literals.
The Java programming language also supports a few special escape sequences for and literals: (backspace), (tab), (line feed), (form feed), (carriage return), (double quote), (single quote), and (backslash).
There's also a special literal that can be used as a value for any reference type. may be assigned to any variable, except variables of primitive types. There's little you can do with a value beyond testing for its presence. Therefore, is often used in programs as a marker to indicate that some object is unavailable.
Finally, there's also a special kind of literal called a class literal, formed by taking a type name and appending "; for example, . This refers to the object (of type ) that represents the type itself.
Using Underscore Characters in Numeric Literals
In Java SE 7 and later, any number of underscore characters () can appear anywhere between digits in a numerical literal. This feature enables you, for example. to separate groups of digits in numeric literals, which can improve the readability of your code.
For instance, if your code contains numbers with many digits, you can use an underscore character to separate digits in groups of three, similar to how you would use a punctuation mark like a comma, or a space, as a separator.
The following example shows other ways you can use the underscore in numeric literals:
You can place underscores only between digits; you cannot place underscores in the following places:
- At the beginning or end of a number
- Adjacent to a decimal point in a floating point literal
- Prior to an or suffix
- In positions where a string of digits is expected
The following examples demonstrate valid and invalid underscore placements (which are highlighted) in numeric literals:
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