Basic design structure of java

Java is case sensitive;

The main method must be declared public, and each application has one and only one main method;

General syntax used by java: object.method(parameters)

Java programs comments

  • Single-Line Comment: //
  • Multiline Comment: /* */

Java data type

8 primitive type:

  • int
  • short
  • long
  • byte
  • float
  • double
  • char
  • boolean

Java variable

Each variable has a type. After a variable is declared, the variable must be initialized with an assignment statement.

Java constant

Use the keyword final to indicate a constant.

Java enumeration

Includes a limited number of named values.

enum Size {SMALL, MEDIUM, LARGE, EXTRA_LARGE};

Java string

A java string is a sequence of Unicode characters.

- Substring
    String.substring()
- Join
    * Allow connection with +
    * Use the join method
- Empty string "" and null string
    * An empty string is a java object with a length of 0 and an empty content;
    * Null string, no object is currently associated with null;

Java array

An array is a data structure that stores a collection of values ​​of the same type.

When declaring array variables, you need to specify the array type, such as int[] a;

Array initialization: a = new int[] {1,23,44,5,67};

Multidimensional arrays (array of arrays): int[][] a = {{1,2},{4,6}};

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