type arrayName[];
  type[] arrayName;

int demoArray[];
int[] demoArray;

  type arrayName[] = new type[arraySize];

int demoArray[] = new int[3];

// 静态初始化
// 静态初始化的同时就为数组元素分配空间并赋值
int intArray[] = {1,2,3,4};
String stringArray[] = {"微学苑", "http://www.weixueyuan.net", "一切编程语言都是纸老虎"};
// 动态初始化
float floatArray[] = new float[3];
floatArray[0] = 1.0f;
floatArray[1] = 132.63f;
floatArray[2] = 100F;

  arrayName[index];

import java.util.*;
public class Demo {
  public static void main(String[] args){
    int intArray[] = new int[5];
    long total = 0;
    int len = intArray.length;
    
    // 给数组元素赋值
    System.out.print("请输入" + len + "个整数，以空格为分隔：");
    Scanner sc = new Scanner(System.in);
    for(int i=0; i<len; i++){
      intArray[i] = sc.nextInt();
    }
    
    // 计算数组元素的和
    for(int i=0; i<len; i++){
      total += intArray[i];
    }
    
    System.out.println("所有数组元素的和为：" + total);
  }
}

int arrayDemo[] = {1, 2, 4, 7, 9, 192, 100};
for(int i=0,len=arrayDemo.length; i<len; i++){
  System.out.println(arrayDemo[i] + ", ");
} 

1, 2, 4, 7, 9, 192, 100,

for( arrayType varName: arrayName ){
  // Some Code
}

int arrayDemo[] = {1, 2, 4, 7, 9, 192, 100};
for(int x: arrayDemo){
  System.out.println(x + ", ");
}

int intArray[ ][ ] = { {1,2}, {2,3}, {4,5} };
int a[ ][ ] = new int[2][3];
a[0][0] = 12;
a[0][1] = 34;
// ......
a[1][2] = 93;

int intArray[ ][ ] = { {1,2}, {2,3}, {3,4,5} };
int a[ ][ ] = new int[2][ ];
a[0] = new int[3];
a[1] = new int[5];

public class Demo {
  public static void main(String[] args){
    // 第一个矩阵（动态初始化一个二维数组）
    int a[][] = new int[2][3];
    // 第二个矩阵（静态初始化一个二维数组）
    int b[][] = { {1,5,2,8}, {5,9,10,-3}, {2,7,-5,-18} };
    // 结果矩阵
    int c[][] = new int[2][4];
    
    // 初始化第一个矩阵
    for(int i=0; i<2; i++)
      for(int j=0; j<3 ;j++)
        a[i][j] = (i+1) * (j+2);
    
    // 计算矩阵乘积
    for (int i=0; i<2; i++){
      for (int j=0; j<4; j++){
        c[i][j]=0;
        for(int k=0; k<3; k++)
          c[i][j] += a[i][k] * b[k][j];
      }
    }
    // 输出结算结果
    for(int i=0; i<2; i++){
      for (int j=0; j<4; j++)
        System.out.printf("%-5d", c[i][j]);
      System.out.println();
    }
  }
}

25  65  14  -65 
50  130 28  -130

  String stringName = "string content";

String url = "http://www.weixueyuan.net";
String webName = "微学苑";

public class Demo {
  public static void main(String[] args){
    String stuName = "小明";
    int stuAge = 17;
    float stuScore = 92.5f;
    
    String info = stuName + "的年龄是 " + stuAge + "，成绩是 " + stuScore;
    System.out.println(info);
  }
}

小明的年龄是 17，成绩是 92.5

String str = "Hello ";
str += "World!";

String stringName = new String("string content");

String url = new String(http://www.weixueyuan.net);

String str1 = "微学苑";
String str2 = "weixueyuan";
System.out.println("The lenght of str1 is " + str1.length());
System.out.println("The lenght of str2 is " + str2.length());

The lenght of str1 is 3
The lenght of str2 is 10

String str = "123456789";
System.out.println(str.charAt(0) + "  " + str.charAt(5) + "  " + str.charAt(8));

1  6  9

String str = "weixueyuan";
System.out.println(str.contains("yuan"));

true

String str1 = "The url of weixueyuan is www.weixueyuan.net!";
String str2 = str1.replace("weixueyuan", "微学苑");
System.out.println(str1);
System.out.println(str2);

The url of weixueyuan is www.weixueyuan.net!
The url of 微学苑 is www.微学苑.net!

import java.util.*;
public class Demo {
  public static void main(String[] args){
    String str = "wei_xue_yuan_is_good";
    String strArr[] = str.split("_");
    System.out.println(Arrays.toString(strArr));
  }
}

[wei, xue, yuan, is, good]