注释

单行注释 //

多行注释 /**/

文档注释 /** */

关键字

数据类型

基本数据类型（8种）

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

1 byte = 8 bit;

public class Hello {
    public static void main(String[] args){
        // 二进制 0b 八进制 0 十进制 十六进制 0x 0~9 A~F
        int a = 0b11;
        int b = 037;
        int c = 0;
        int d = 0xff;
        System.out.println(a);//3
        System.out.println(b);//31
        System.out.println(c);//0
        System.out.println(d);//255
    }
}

引用类型

new Object();

scanner

基本语法：

Scanner s = new Scanner(System.in);

1. next() 遇到空格就结束
2. nextLine() 以enter结束

break、continue、goto

break 退出当前循环

continue 退出当次循环，执行后面的循环

数组

//创建数组
int[] arr = new int[10];
//静态初始化
int[] a = {1,2,3,4};

二维数组

//二维数组
String[][] arrStr = new String[2][5];
//二维数组静态初始化
String[][] b = {{"a","b","c"},{"d","e","f"},{"h","i"}};
System.out.println(b[2][1]);//i
System.out.println(b[0].length);//3
System.out.println(b[2].length);//2

Arrays类

常用方法：

• fill() 填充数组

• int[] arr = new int[10];
  Arrays.fill(arr,0);
  System.out.println(Arrays.toString(arr));//[0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
  

• sort() 排序

• int[] arr = {5,64,65,6,4,67,8,76,46,7};
  Arrays.sort(arr);
  System.out.println(Arrays.toString(arr));//[4, 5, 6, 7, 8, 46, 64, 65, 67, 76]
  

• equals() 判断数组元素值是否相等

• int[] a = {5,64,65};
  int[] b = {5,64,65};
  System.out.println(Arrays.equals(a,b));//true
  int[] a = {5,64,65};
  int[] b = {5,64,66};
  System.out.println(Arrays.equals(a,b));//false
  

• binarySearch() 对排序好的数组进行二分法查找

• Arrays.binarySearch(a,1);	
  

冒泡排序

    int[] a = {5,64,65,78,7,8,2};
    int min = 0;
    for (int i = 0; i < a.length; i++) {
        for (int j = i+1; j < a.length; j++) {
           if(a[i] > a[j]){
               min = a[j];
               a[j] = a[i];
               a[i] = min;
           }
        }
    }
    System.out.println(Arrays.toString(a));//[2, 5, 7, 8, 64, 65, 78]
}