Java Variable and Constant

Java Variable

  • A variable is a location in your computer's memory in which you can store a value and from which you can later retrieve that value.
  • Your computer's memory is normally Random Access Memory (RAM).
  • A variable must always be defined inside a Java class.
  • When you define a variable in Java, you must tell the compiler what kind of variable it is. (this is usually referred to as variable type).

Java Primitive variable types

  • Java works with Primitive variable types, which represent simple values that have built-in functionality in the language.
  • They are fixed elements, such as characters, integers and floating-point.
    Primitive types in Java:
    Type Definition
    boolean true or false
    char 16-bit, Unicode character
    byte 8-bit, signed, two's complement integer
    short 16-bit, signed, two's complement integer
    int 32-bit, signed, two's complement integer
    long 64-bit, signed, two's complement integer
    double 64-bit, 1.7e-308 – 1.7e+308, floating point value
    float 32-bit, 3.4e-38 -- 3.4e+38, floating-point value
    Variable declaration example:
    int foo;
    double d1, d2;
    boolean isFun;
    Variable declaration with initialization example:
    int foo = 42;
    double d1 = 3.14, d2 = 2 * 3.14;
    boolean isFun = true;
    Integer literals example:
    int i1 = 1230;   // specified in decimal (base 10) 
    int i2 = 01230;  // specified in octal (base 8)          // i2 = 664 decimal 
    int i3 = 0xFFFF; // specified in hexadecimal (base 16)   // i3 = 65535 decimal 
    Automatic casting/converting example:
    long l = 13L;    // Int. literals are of type int 
                     // unless they are suffixed with an L
    long l = 13;     // Equivalent: 13 is converted from type int
    byte b = 42;     // Works fine as long as values < 255
    int i = 43;
    int result = b * i;  // b is promoted to int before multiplication 
    int x = 13;
    byte b = x;           // Compile-time error, explicit cast needed 
    byte b = (byte) x;    // OK - as x is casted to byte
    Floating-point literals example:
    double d = 8.31;      // Floating-point values can be specified in decimal 
    double e = 3.00e+8;   // or specified in scientific notation 
    float f = 8.31F;      // Default of type double unless they 
                          // are suffixed with an f or F 
    float g = 3.00e+8F;;
    Character literals example:
    char a = 'a';            // Specified either as a single-quoted character 
                             // or
    char newline = '\n';     // as an escaped ASCII 
                             // or
    char smiley = '\u263a';  // written with special Unicode escape sequences 
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