Language Basics

the traditional features of the Java, including variables, arrays, data types, operators and control flow

Variables

kinds of variables in Java

• Instance Variables(Non-Static Fields)

  Instance Variables are unique to each instance of a object(class), objects store their individual states in "non-statis fields"

• Class Variables(Static Fields)

  Class Variables is governed by the object(class), regardless of how many times the class has been instantiated.

• Local Variables

  A method will often store its temporary state in local variables. Local variables are absolutely only visible to the methods in whhich they are declared,

• Parameters

Primitive Data Types

The Java programming language is statically-typed, which means that all variables must first be declared before they can be used.

Data Type	Default Value(for fields)
byte	0
short	0
int	0
long	0
float	0.0
double	0.0
char	'\u0000'
boolean	false

Local variables are slightly different; the compiler never ever never assgin a default value to an unitialized local variable. You musk make sure assign a local variable a value before you attempt to use it or else result in compile-time error

• Using Underscore Characters in Numeric Literals to Imporve the readability of code.

  Place underscores only between digits. you cannot place underscores in the following places;

   1. At the beginning or end of a number
   2. Adjacent to a decimal point in a floating point literal
   3. Prior to an F or L suffix
   4. In positions where a string of digits is expected
  

  long creditCardNumber = 1234_6123_2312_2332L; // ✅
  float PI = 3.14_15F; //✅
  float pi = 3_.1415F; //❌
  int x1 = 52_; //❌
  int x2 = Ox_52; //❌
  int x3 = Ox5_2; //❌
  

Arrays

An array is a container object that holds a fixed number of values of a single type.The length of an array is established when the array is created.

// Create an array of integers with 10 length
int[] anArray = new int[10];
// Create an array with assigned elements
int[] arrInt = {
  100, 200, 300
    400, 500, 600
}

Bullet point

1. The term "instance variable" is another name for non-static field.
2. The term "class variable" is another name for static field.
3. A local variable store termporary state; it is declared inside a method.
4. A variable declared within the openming and closing parenthesis of a method is called a parameter.
5. What are the eight primitive data types supported by the Java programming language? byte，short，int，long，float，double，boolean，char.
6. Character strings are represented by the class java.lang.String.
7. An array is a container object that holds a fixed number of values of a single value.

Operators

Assignment, Arithmetic, and Unary Operators

• The Arithmetic Operators

The languages provides operators that perform addition, subtraction, multiplication, and division.

Operators	Description
+	Additive operator(also used for String concatenation)
-	Subtraction operator
*	Multiplication operator
/	Division operator
%	Remainder operator

• The Unary Operators

The unary operators require only one operand; they perform various operations such as incrementing/decrementing a value by one, negating an expression. or inverting the value of a boolean.

Operator	Description
+	Unary plus operator; indicates positive value
-	Unary minus operator; negates an expression
++	Increment operator; increments a value by 1
--	Decrement operator; decrements a value by 1
!	Logical complement operator; inverts the value of a boolean

• Equality, Relational, and Conditional Operators

Operator	Description
==	equal to
!=	not equal to
>	greater than
>=	greater than or equal to
<	less than
<=	less than or equal to

• The conditional Operators

  • && and || perform Conditional-AND and Conditional-OR operations on two boolean expressions. These operatos exhibit "short-circuiting" behavior.

  • 【expressions ? doSth(T) : doSth(F)】as shorthand for an 【if-then-else】

  Operator	Description
  &&	Conditional-And
  II	Conditional-OR
  ?:	Ternary(shorthand for if-then-else statement)

• Bitwise and Bit Shift Operators

  Operator	Description
  ~	Unary bitwise complement
  <<	Signed left shift
  >>	Signed right shift
  >>>	Unsigned right shift
  &	Bitwise And
  ^	Bitwise exclusive OR
  I	Bitwise inclusive OR