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.
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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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