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java_language_basic.md

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Language Basic

Variables

  • Instance Variables (Non-Static Fields)
  • Class Variables (Static Fields)
  • Local Variables
  • Parameters

Primitive Data Types

Type Length Range Default
byte 8-bit -128 ~ 127 0
short 16-bit -32,768 ~ 32,767 0
int 32-bit -2^31 ~ 2^31-1 0
long 64-bit -2^63 ~ 2^63-1 0L
float 32-bit single-precision 0.0f
double 64-bit double-precision 0.0d
boolean no precisely defined true/false false
char 16-bit '\u0000' ~ '\uffff' '\u0000'
  • Integer divided by zero throws java.lang.ArithmeticExcaption, while double divided by zero integer is Infinity, or divided by double zero is NaN, and both don't throw any exception.

Note: local variables never assigned a default value. Accessing an uninitialized local variable will result in compile-time error.

Arrays

An array is a container object that holds a fixed number of values of a single type.

Creating, Initializing

// 1
int[] anArray = new int[10];
anArray[0] = 100;
anArray[1] = 200;

// 2
int [] anArray = {100, 200};

Operators

Operator Precedence

Operators Precedence
postfix expr++ expr--
unary ++expr --expr +expr -expr ~ !
multiplicative * / %
additive + -
shift << >> >>>
relational < > <= >= instanceof
equality == !=
bitwise AND &
bitwise exclusive OR ^
bitwise inclusive OR |
logical AND &&
logical OR ||
ternary ? :
assignment = += -= *= /= %= &= ^= |= <<= >>= >>>=

Relational

Because null is not an instance of anything, null instanceof anything always return false.

Logical and Bitwise

  • Priority: ! > && > ||.
  • &, |: both sides will be checked.
  • >>: signed right shift operator that shifts a bit pattern to the right by extending the sign bit with the number of positions to shift by the right-hand operand.
    • -1 >> n => -1.
  • <<: signed left shift operator.
  • >>>: unsigned right shift operator that shifts a zero into the leftmost position.

Control Flow

switch statement

switch works with byte, short, char, int, Enum, Character, Byte, Short, Integer, String (Java 7).

Note: if expression in any switch statement is null, then a NullPointerException is thrown.