java实用类、方法记录--持续更新

r囧r小猫 2023-07-01 08:41 3阅读 0赞

### 文章目录 ###

*  java实用类、方法记录--持续更新
 *   *  StringJoiner（字符串拼接）
     *  StringTokenizer（字符串拆分）
     *  CountDownLatch（同步器）
     *  AtomicInteger（原子类）

# java实用类、方法记录–持续更新 #

*  ## StringJoiner（字符串拼接） ##
    
    1.  当需要使用某些符号拼接多个数据时
        
            StringJoiner stringJoiner = new StringJoiner(",");
            stringJoiner.add("1");
            stringJoiner.add("2");
            stringJoiner.add("3");
        
        > 1,2,3
    2.  增加前后缀
        
            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.  与StringJoiner相反，用于拆分字符串,默认拆分字符是（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.  可以设置把拆分的字符也输出
        
            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.  获取数量
        
            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)定义数量，countDownLatch.countDown()减少数量，countDownLatch.await();等待数量为0时执行，否则一直堵塞，可设置最长堵塞时间
        
            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（原子类） ##
    
    1.  AtomicInteger保证操作时是原子操作
        
        > 举一反三，atomic系列的还有  
        > ![在这里插入图片描述][20200612094758221.png]
        
            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

[20200612094758221.png]: https://img-blog.csdnimg.cn/20200612094758221.png