[Chapter 2] 2.6 Primitive Data Types
Author: David Flanagan
Date: Thu Jul 31 15:47:46 1997

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| Chapter 2 How Java Differs from C |

## 2.6 Primitive Data Types

Java adds `byte` and `boolean` primitive types to the standard set of C types. In addition, it strictly defines the size and signedness of its types. In C, an `int` may be 16, 32, or 64 bits, and a `char` may act signed or unsigned depending on the platform. Not so in Java. In C, an uninitialized local variable usually has garbage as its value. In Java, all variables have guaranteed default values, though the compiler may warn you in places where you rely, accidentally or not, on these default values. Table 2.2 lists Java's primitive data types. The subsections below provide details about these types.

Table 2.2: Java Primitive Data Types
|  |  |  | Min Value
--- | --- | --- | --- | ---
Type | Contains | Default | Size | Max Value
boolean | `true` or `false` | `false` | 1 bit | N.A.
|  |  |  | N.A.
char | Unicode character | `\u0000` | 16 bits | `\u0000`
|  |  |  | `\uFFFF`
byte | signed integer | 0 | 8 bits | -128
|  |  |  | 127
short | signed integer | 0 | 16 bits | -32768
|  |  |  | 32767
int | signed integer | 0 | 32 bits | -2147483648
|  |  |  | 2147483647
long | signed integer | 0 | 64 bits | -9223372036854775808
|  |  |  | 9223372036854775807
float | IEEE 754 | 0.0 | 32 bits | +/-3.40282347E+38
| floating-point |  |  | +/-1.40239846E-45
double | IEEE 754 | 0.0 | 64 bits | +/-1.79769313486231570E+308
| floating-point |  |  | +/-4.94065645841246544E-324

### The boolean Type

`boolean` values are not integers, may not be treated as integers, and may never be cast to or from any other type. To perform C-style conversions between a `boolean` value `b` and an `int` `i`, use the following code:

    b = (i != 0);   // integer-to-boolean: non-0 -> true; 0 -> false;
    i = (b)?1:0;    // boolean-to-integer: true -> 1; false -> 0;

### The char Type

`char` values represent characters. Character literals may appear in a Java program between single quotes. For example:

    char c = 'A';

All of the standard C character escapes, as well as Unicode escapes, are also supported in character literals. For example:

    char newline = '\n', apostrophe = '\", delete = '\377', aleph='\u05D0';

Values of type `char` do not have a sign. If a `char` is cast to a `byte` or a `short`, a negative value may result.

The `char` type in Java holds a two-byte Unicode character. While this may seem intimidating to those not familiar with Unicode and the techniques of program internationalization, it is in fact totally transparent. Java does not provide a way to compute the size of a variable, nor does it allow any sort of pointer arithmetic. What this means is that if you are only using ASCII or Latin-1 characters, there is no way to distinguish a Java `char` from a C `char`.

### Integral Types

The integral types in Java are `byte`, `short`, `char`, `int`, and `long`. Literals for these types are written just as they are in C. All integral types, other than `char`, are signed. There is no `unsigned` keyword as there is in C. It is not legal to write `long` `int` or `short` `int` as it is in C. A `long` constant may be distinguished from other integral constants by appending the character `l` or `L` to it.

Integer division by zero or modulo zero causes an `ArithmeticException` to be thrown. [3]

> [3] Exceptions signal errors in Java. Exception handling is described later in this chapter.

### Floating-Point Types

The floating-point types in Java are `float` and `double`. Literals for these types are written just as they are in C. Literals may be specified to be of type `float` by appending an `f` or `F` to the value; they may be specified to be of type `double` by appending a `d` or `D`.

`float` and `double` types have special values that may be the result of certain floating-point operations: positive infinity, negative infinity, negative zero and not-a-number. The `java.lang.Float` and `java.lang.Double` classes define some of these values as constants: `POSITIVE_INFINITY`, `NEGATIVE_INFINITY`, and `NaN`.

`NaN` is unordered--comparing it to any other number, including itself, yields `false`. Use `Float.isNaN()` or `Double.isNaN()` to test for `NaN`. Negative zero compares equal to regular zero (positive zero), but the two zeros may be distinguished by division: one divided by negative zero yields negative infinity; one divided by positive zero yields positive infinity.

Floating-point arithmetic never causes exceptions, even in the case of division by zero.

### String Literals

Strings in Java are not a primitive type, but are instances of the `String` class. However, because they are so commonly used, string literals may appear between quotes in Java programs, just as they do in C. When the compiler encounters such a string literal, it automatically creates the necessary `String` object.

Unicode and Character Escapes |  | Reference Data Types