序列化类：

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import java.io.Serializable;
public class User implements Serializable{}

JSONObject 中获取所有的 key

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<!--JSONObject-->
<dependency>  
   <groupId>net.sf.json-lib</groupId>  
   <artifactId>json-lib</artifactId>  
   <version>2.4</version>  
   <classifier>jdk15</classifier>  
</dependency>

Iterator keys = jsonObject.keys();
while(keys.hasNext()){
    String key = keys.next().toString();
    System.out.println("key:"+key);
}；

UUID

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UUID uuid = UUID.randomUUID();  // java uuid

java 端随机数 

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int random = new Random().nextInt(800);

获得系统时间 

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long timestamp = System.currentTimeMillis();

测时间 - 性能–代码执行时间 

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long begin_time = System.currentTimeMillis();
long end_time = System.currentTimeMillis();
long time = end_time- begin_time ;
String result = " 用时："+(time > 60000 ? (time / 60000) + " 分钟 " : time > 1000 ? (time / 1000) + " 秒 " : time + " 毫秒 ");

随机数

  • 获得一组不重复的随机数组 

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    /**
     * 获得一组不重复的随机数组 
     *
     * @param length
     * @return
     */
    public int[] getRandom(int length) {
        int[] numbers = new int[length];

        for (int i = 0; i < numbers.length; i++) {
            int num = 0;
            while (true) {
                boolean tag = false;
                num = (int) (Math.floor(Math.random() * length)) + 1;
                for (int j = 0; j < numbers.length; j++) {
                    if (numbers[j] == num) {
                        tag = true;
                        break;
                    }
                }
                if (!tag) {
                    break;
                }
            }
            numbers[i] = num;
        }

        for (int i = 0; i < numbers.length; i++) {
            numbers[i] = numbers[i] - 1;
        }
        return numbers;
    }

  • 根据传递过来的长度，随机分配 60S 内不重复的数组 

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    /**
     * 根据传递过来的长度，随机分配 60S 内不重复的数组 
     *
     * @param length
     * @return
     */
    public int[] randomNextMinute(int length) {
        int[] arr = new int[length];
        for (int i = 0; i < arr.length; i++) {
            int ran;
            while (true) {
                ran = (int) (Math.random() * 60);
                if (ran > 60) {
                    ran = ran - 60;
                }
                boolean tag = false;
                for (int j = 0; j < arr.length; j++) {
                    if (arr[j] == ran) {
                        tag = true;
                    }
                }
                if (!tag) {
                    break;
                }
            }
            arr[i] = ran;
        }
        return arr;
    }

  • 打乱有序数组 

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    // 打乱有序数组 
    Random random = new Random();
    for (int i = allMoney.length - 1; i >= 0; i--) {
        index = random.nextInt(allMoney.length);
        int temp = allMoney[i];
        allMoney[i] = allMoney[index];
        allMoney[index] = temp;
    }