“Java”的版本间的差异

public class HelloWorld{ 
    public static void main(String[] args) {  
        System.out.println("Hello World!"); 
    }
}

import java.util.Arrays; 
 
public class Hello { 
    public static void main(String[] args) {  
        String pool[] = {"dog", "cat", "pig", "main", "fish"};
        System.out.println(Arrays.asList(pool));
    }
}

int i = 123;
 
String s = String.valueOf(i);
 
String s = Integer.toString(i);
 
String s = i + "";
 
//字符转数字
String str = "123456";
 
i = Integer.parseInt(str);

String A = "abcd";
String B = "abcd"; 
 
A == B;       //ture   
A.equals(B);  //true
 
String A = new String("abcd");
String B = new String("abcd");
A == B;        //false  
A.equals(B);   //true

List<String[]> users = null;

List<String[]> users = new LinkedList<String[]>();

Object principal = SecurityContextHolder.getContext().getAuthentication().getPrincipal();
String username = "";
 
if (principal instanceof UserDetails) {
    username = ((UserDetails) principal).getUsername();
} else {
    username = principal.toString();
}
 
System.out.println(username);

public class Pojo{
    private String a;
    private int b;
}
 
@RequestMapping(method = RequestMethod.POST)
public String processSubmit(@ModelAttribute("pojo") Pojo pojo) {
    return "helloWorld";
}

@RequestMapping(method = RequestMethod.GET)
public String get(HttpServletRequest request, HttpServletResponse response) {
    System.out.println(request.getParameter("a"));
    return "helloWorld";
}

Random random    = new Random(System.currentTimeMillis());
int index_random = random.nextInt(listItem.size());

private String guid() {
    UUID uuid = UUID.randomUUID();
    String str = uuid.toString();
 
    // 去掉"-"符号
    String temp = str.substring(0, 8) + str.substring(9, 13) + str.substring(14, 18) + str.substring(19, 23) + str.substring(24);
    return temp;
}

double pi = 3.1415927;//pi   
 
// 取一位整数   
System.out.println(new DecimalFormat("0").format(pi));// 3   
 
// 取一位整数和两位小数   
System.out.println(new DecimalFormat("0.00").format(pi));// 3.14   
 
// 取两位整数和三位小数，整数不足部分以0填补。   
System.out.println(new DecimalFormat("00.000").format(pi));// 03.142   
 
// 取所有整数部分   
System.out.println(new DecimalFormat("#").format(pi));// 3   
 
// 以百分比方式计数，并取两位小数   
System.out.println(new DecimalFormat("#.##%").format(pi));// 314.16%   
 
long c = 299792458;
 
// 显示为科学计数法，并取五位小数   
System.out.println(new DecimalFormat("#.#####E0").format(c));// 2.99792E8   
 
// 显示为两位整数的科学计数法，并取四位小数   
System.out.println(new DecimalFormat("00.####E0").format(c));// 29.9792E7   
 
// 每三位以逗号进行分隔。   
System.out.println(new DecimalFormat(",###").format(c));// 299,792,458   
 
// 将格式嵌入文本   
System.out.println(new DecimalFormat("光速大小为每秒,###米。").format(c));

private String RandomString(int length, String type) {
    String number = "0123456789";
    String str = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
    Random random = new Random();
    StringBuffer sb = new StringBuffer();
 
    for (int i = 0; i < length; i++) {
        if (type.equals("number")) {
            int num = random.nextInt(number.length());
            sb.append(number.charAt(num));
        } else {
            int num = random.nextInt(str.length());
            sb.append(str.charAt(num));
        }
    }
 
    return sb.toString();
}

    // 密钥
    private final static String secretKey = "key123";
    private final static String salt = "0123456789abcdef" ;//KeyGenerators.string().generateKey();
 
    /**
     * 加密
     *
     * @param plainString 明文
     * @return
     */
    private static String encrypt(String plainString) {
        // 明文
        byte[] byteArray = plainString.getBytes();
 
        // 加密，设置密钥和随机数
        byte[] cipherArrayTemp = Encryptors.standard(secretKey, salt).encrypt(byteArray);
        byte[] cipherArray = Base64.encode(cipherArrayTemp);
        return new String(cipherArray);
    }
 
    /**
     * 解密
     *
     * @param cipherString 密文
     * @return
     */
    private static String decrypt(String cipherString) {
        // 密文
        byte[] byteArray = cipherString.getBytes();
        byte[] plainArrayTemp = Base64.decode(byteArray);
 
        // 解密
        byte[] plainArray = Encryptors.standard(secretKey, salt).decrypt(plainArrayTemp);
        return new String(plainArray);
    }

@RequestMapping(value = "batchCardNoExport", method = RequestMethod.GET)
public void batchCardNoExport(HttpServletRequest request, HttpServletResponse response) throws Exception {
    // 创建Excel的工作书册 Workbook,对应到一个excel文档
    HSSFWorkbook wb = new HSSFWorkbook();
 
    // 创建Excel的工作sheet,对应到一个excel文档的tab
    HSSFSheet sheet = wb.createSheet("sheet1");
 
    HSSFRow row;
    HSSFCell cell;
 
    for (int i = 0; i < 60; i++) {
        row = sheet.createRow(i); // 创建Excel的sheet的一行
        for (int j = 0; j < 30; j++) {
            cell = row.createCell(j); // 创建一个Excel的单元格
            cell.setCellValue("hello world " + i + " " + j);
        }
    }
 
    response.setContentType("application/vnd.ms-excel");
    response.setHeader("Content-Disposition", "attachment; filename=filename.xls");
    wb.write(response.getOutputStream()); // Write workbook to response.
    wb.close();
}

import java.util.*; 
import java.text.SimpleDateFormat;
 
public class hello { 
 
 
    public static void main(String[] args) {  
 
        int[] ebbing = {1, 2, 4, 7, 15, 30, 50, 70, 100, 150, 200, 150, 200, 300, 400};
 
        getToday((long)ebbing[0] * 3600 * 24 * 1000); 
        getToday((long)ebbing[1] * 3600 * 24 * 1000); 
        getToday((long)ebbing[2] * 3600 * 24 * 1000); 
        getToday((long)ebbing[3] * 3600 * 24 * 1000); 
        getToday((long)ebbing[4] * 3600 * 24 * 1000); 
        getToday((long)ebbing[5] * 3600 * 24 * 1000); 
        getToday((long)ebbing[6] * 3600 * 24 * 1000); 
        getToday((long)ebbing[7] * 3600 * 24 * 1000); 
        getToday((long)ebbing[8] * 3600 * 24 * 1000); 
    } 
 
    // int为整数类型，在存储的时候，用4个字节存储，范围为-2,147,483,648到2,147,483,647。
    // 原用的是getToday(int offset_ms)，这样在第6个日期，就超出范围了。
    public static String getToday(long offset_ms) {
 
    	SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd"); 
		Date date = new Date(System.currentTimeMillis() + offset_ms);
		String today = dateFormat.format(date);
 
        System.out.println(offset_ms + " " + today); 
 
		return today;
    } 
}