Basic grammar

Common naming conventions

  • Package name: Use lowercase letters xxXYYYZZz for multiple words
  • Class name, interface name: Uppercase XxxYyyZzz (big hump)
  • Variable name, method name: When multiple words are formed, the first word starts with lower case and each following word starts with upper case xxxYyyZzz
  • Constant name: all letters are capitalized and multiple words are connected by _

variable

The data type

Eight basic data types +

Automatic type promotion

A byte, char, or short operation results in an int. For example, short+char or short+short requires an int

Cast casting

Reverse operation of automatic type promotion to change a large type to a small type

Long

You need to add an L after the number to store larger numbers. Float, again, you have to add F

char

Char is converted to int for addition

string

It is a reference data type and can only be concatenated. A string concatenated to any primitive data type results in a string

Scanner

import java.util.Scanner Scanner scanner=new Scanner(System.in); Int num= scanner.nextint () double num=scanner.nextDouble() String s=scanner.next() char c= s.charat (0)Copy the code

Loop label

Before a loop, you can use break or continue to specify that a level of loop is skipped

An array of

Declaration and initialization of one-dimensional arrays
  • Static initialization
Int [] array = new int [] {2} 1001100;Copy the code
  • Dynamic initialization
String[] array=new String[5];
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  • The length of the array
array.length
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  • Default initialization values for array elements

Integer arrays: 0: byte, short, int, and long Floating point arrays: 0.0: float, double: ASCII 0: char Boolean array: false: Boolean String array: null: String

Declaration and initialization of multidimensional arrays
  • Static initialization
Int [] [] array = new int [] [] {{1, 2}, {3, 4}}Copy the code
  • Dynamic initialization
int[][] array=new int[2][3]
int[][] array=new int[2][]
array[0]=new int[3]
array[1]=new int [4]
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  • The length of the array
Int [][] array=new int[2][3] array.length// is 2 aray[0]. Length // is 3Copy the code
  • Multi-dimensional array traversal
for(int i=0; i<array.length; i++){ for(int j=0; j<array[i].length; j++){ System.out.println(array[i][j]); }}Copy the code
The Arrays tools

  • Call way
Int a [] = new int [] {1, 2, 3}; Int [b] = new int [] {4 and 6}; Arrays.equals(a,b); Int [c] = new int [] {1, 2, 3}; System.out.println(Arrays.toString(a));Copy the code