Organized memo in the head (Java --Data type)

My Java environment

Java data type

Primitive type (use the value itself, null cannot be assigned.)

Reference type (handles a reference to an instance)


Numerical notation using underscore

int value = 123_456;

The display result is


Identifier naming convention

Type inference (var)

Type inference is done at compile time.


var value = 123;
var value = method();
var value = new ArrayList<>();


var value;
var value = null;
var value = {1, 2, 3};
var value =Lambda expression

var classA = new ClassA();
classA = new ClassB();

mutable and immutable



Type range

byte < short < int < long < float < double

Baishoiro Fuda

Type conversion

Explicitly cast from large to small.

int value1 = 123;
short value2 = (int)value1;

Identity and equivalence

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