java實用類、方法記錄--持續更新

java實用類、方法記錄–持續更新

• StringJoiner（字符串拼接）

  1. 當需要使用某些符號拼接多個數據時

     StringJoiner stringJoiner = new StringJoiner(",");
     stringJoiner.add("1");
     stringJoiner.add("2");
     stringJoiner.add("3");
     

     1,2,3

  2. 增加前後綴

     StringJoiner stringJoiner = new StringJoiner(",", "(", ")");
     stringJoiner.add("1");
     stringJoiner.add("2");
     stringJoiner.add("3");
     System.out.println(stringJoiner.toString());
     

     (1,2,3)

     StringJoiner stringJoiner = new StringJoiner("','", "('", "')");
     stringJoiner.add("1");
     stringJoiner.add("2");
     stringJoiner.add("3");
     System.out.println(stringJoiner.toString());
     

     (‘1’,‘2’,‘3’)

  ---

• StringTokenizer（字符串拆分）

  1. 與StringJoiner相反，用於拆分字符串,默認拆分字符是（空格 \t\n\r\f）

     String str = "1231\t1\n3\f45 a";
     StringTokenizer stringTokenizer = new StringTokenizer(str);
     while (stringTokenizer.hasMoreTokens()) {
         System.out.println(stringTokenizer.nextToken());
     }
     

     1231
     1
     3
     45
     a

  2. 可以指定拆分字符

     String str = "1231 1,3,45 a";
     StringTokenizer stringTokenizer = new StringTokenizer(str, " ,");
     while (stringTokenizer.hasMoreTokens()) {
         System.out.println(stringTokenizer.nextToken());
     }
     

     1231
     1
     3
     45
     a

  3. 可以設置把拆分的字符也輸出

     String str = "12311,3,45a";
     StringTokenizer stringTokenizer = new StringTokenizer(str, ",", true);
     while (stringTokenizer.hasMoreTokens()) {
         System.out.println(stringTokenizer.nextToken());
     }
     

     1231
     1
     ,
     3
     ,
     45
     a

  4. 修改拆分的字符

     String str = "1231:1,3,45:a";
     StringTokenizer stringTokenizer = new StringTokenizer(str, ",");
     while (stringTokenizer.hasMoreTokens()) {
         String next = stringTokenizer.nextToken();
         System.out.println(next);
         if (next.equals("3")) {
             stringTokenizer.nextToken(":");
         }
     }
     

     1231:1
     3
     a

  5. 獲取數量

     String str = "1231:1,3,45:a";
     StringTokenizer stringTokenizer = new StringTokenizer(str, ",");
     System.out.println(stringTokenizer.countTokens());
     

     3

---

• CountDownLatch（同步器）

  1. new CountDownLatch(2)定義數量，countDownLatch.countDown()減少數量，countDownLatch.await();等待數量爲0時執行，否則一直堵塞，可設置最長堵塞時間

     public class Test{
     
         private static CountDownLatch countDownLatch = new CountDownLatch(2);
     
         public static void main(String[] args) throws Exception{
             new Thread(Test::runIncrement).start();
             new Thread(Test::runDecrement).start();
             countDownLatch.await();
             System.out.println("main");
         }
     
         private static void runIncrement() {
             sleep();
             System.out.println("runIncrement");
             countDownLatch.countDown();
         }
     
         private static void runDecrement() {
             sleep();
             System.out.println("runDecrement");
             countDownLatch.countDown();
         }
     
         private static void sleep() {
             try {
                 Thread.sleep(100);
             } catch (InterruptedException e) {
                 e.printStackTrace();
             }
         }
     }
     

     runDecrement
     runIncrement
     main

     或

     runIncrement
     runDecrement
     main

---

• AtomicInteger（原子類）

  1. AtomicInteger保證操作時是原子操作

     舉一反三，atomic系列的還有
     

     public class Test{
     
         private static AtomicInteger atomicInteger = new AtomicInteger(2);
         private static Integer integer = 2;
         private static CountDownLatch countDownLatch = new CountDownLatch(2);
     
         public static void main(String[] args) throws Exception{
             new Thread(Test::runIncrement).start();
             new Thread(Test::runDecrement).start();
             countDownLatch.await();
             System.out.println(integer);
             System.out.println(atomicInteger.get());
         }
     
         private static void runIncrement() {
             for (int i = 0; i < 100000; i++) {
                 integer += 1;
                 atomicInteger.getAndIncrement();
             }
             countDownLatch.countDown();
         }
     
         private static void runDecrement() {
             for (int i = 0; i < 100000; i++) {
                 integer -= 1;
                 atomicInteger.getAndDecrement();
             }
             countDownLatch.countDown();
         }
     }
     

     42713(不定值)
     2