(资料图)

::方法使用

条件：lambada表达式的主体仅包含一个表达式，且lambada表达式只调用一个已经存在的方法；被引用的方法的参数列表与lambada表达式的输入输出一致

以下是Java 8中方法引用的一些语法：

静态方法引用（static method）语法：classname::methodname例如：Person::getAge对象的实例方法引用语法：instancename::methodname例如：System.out::println对象的超类方法引用语法： super::methodname类构造器引用语法： classname::new例如：ArrayList::new数组构造器引用语法： typename[]::new例如： String[]:new

DataStreamSource kafkaDS = env.addSource(MyKafkaUtil.getKafkaConsumer(sourceTopic, groupId));kafkaDS.map(line->{return JSON.parseObject(line);});//Lambda 简写kafkaDS.map(JSON::parseObject);

@Testvoid printTest1() {    List list = Arrays.asList("a", "b", "c", "d");    System.out.println("for  => ");    for (String item : list) {        AcceptMethod.printValue(item);    }    System.out.println("forEach => ");    list.forEach(item -> AcceptMethod.printValue(item));    System.out.println("forEach => ：：");    //list.forEach(new AcceptMethod()::printValue); //非静态方法    list.forEach(AcceptMethod::printValue);    System.out.println("forEach list => ：：");    List loginUserList = new ArrayList<>();    LoginUser loginUser = new LoginUser();    loginUser.setOs("iOS");    loginUserList.add(loginUser);    loginUser = new LoginUser();    loginUser.setOs("Android");    loginUserList.add(loginUser);    loginUserList.forEach(AcceptMethod::printList);}public static class AcceptMethod {    public static void printValue(String str) {        System.out.println("print value : " + str);    }    public static void printList(LoginUser map) {        System.out.println("print value : " + map.getOs());    }}

Stream 示例

public class Java8Tester {   public static void main(String args[]){      System.out.println("使用 Java 7: ");              // 计算空字符串      List strings = Arrays.asList("abc", "", "bc", "efg", "abcd","", "jkl");      System.out.println("列表: " +strings);      long count = getCountEmptyStringUsingJava7(strings);              System.out.println("空字符数量为: " + count);      count = getCountLength3UsingJava7(strings);              System.out.println("字符串长度为 3 的数量为: " + count);              // 删除空字符串      List filtered = deleteEmptyStringsUsingJava7(strings);      System.out.println("筛选后的列表: " + filtered);              // 删除空字符串，并使用逗号把它们合并起来      String mergedString = getMergedStringUsingJava7(strings,", ");      System.out.println("合并字符串: " + mergedString);      List numbers = Arrays.asList(3, 2, 2, 3, 7, 3, 5);              // 获取列表元素平方数      List squaresList = getSquares(numbers);      System.out.println("平方数列表: " + squaresList);      List integers = Arrays.asList(1,2,13,4,15,6,17,8,19);              System.out.println("列表: " +integers);      System.out.println("列表中最大的数 : " + getMax(integers));      System.out.println("列表中最小的数 : " + getMin(integers));      System.out.println("所有数之和 : " + getSum(integers));      System.out.println("平均数 : " + getAverage(integers));      System.out.println("随机数: ");              // 输出10个随机数      Random random = new Random();              for(int i=0; i < 10; i++){         System.out.println(random.nextInt());      }              System.out.println("使用 Java 8: ");      System.out.println("列表: " +strings);              count = strings.stream().filter(string->string.isEmpty()).count();      System.out.println("空字符串数量为: " + count);              count = strings.stream().filter(string -> string.length() == 3).count();      System.out.println("字符串长度为 3 的数量为: " + count);              filtered = strings.stream().filter(string ->!string.isEmpty()).collect(Collectors.toList());      System.out.println("筛选后的列表: " + filtered);              mergedString = strings.stream().filter(string ->!string.isEmpty()).collect(Collectors.joining(", "));      System.out.println("合并字符串: " + mergedString);              squaresList = numbers.stream().map( i ->i*i).distinct().collect(Collectors.toList());      System.out.println("Squares List: " + squaresList);      System.out.println("列表: " +integers);              IntSummaryStatistics stats = integers.stream().mapToInt((x) ->x).summaryStatistics();              System.out.println("列表中最大的数 : " + stats.getMax());      System.out.println("列表中最小的数 : " + stats.getMin());      System.out.println("所有数之和 : " + stats.getSum());      System.out.println("平均数 : " + stats.getAverage());      System.out.println("随机数: ");              random.ints().limit(10).sorted().forEach(System.out::println);              // 并行处理      count = strings.parallelStream().filter(string -> string.isEmpty()).count();      System.out.println("空字符串的数量为: " + count);   }       private static int getCountEmptyStringUsingJava7(List strings){      int count = 0;              for(String string: strings){                 if(string.isEmpty()){            count++;         }      }      return count;   }       private static int getCountLength3UsingJava7(List strings){      int count = 0;              for(String string: strings){                 if(string.length() == 3){            count++;         }      }      return count;   }       private static List deleteEmptyStringsUsingJava7(List strings){      List filteredList = new ArrayList();              for(String string: strings){                 if(!string.isEmpty()){             filteredList.add(string);         }      }      return filteredList;   }       private static String getMergedStringUsingJava7(List strings, String separator){      StringBuilder stringBuilder = new StringBuilder();              for(String string: strings){                 if(!string.isEmpty()){            stringBuilder.append(string);            stringBuilder.append(separator);         }      }      String mergedString = stringBuilder.toString();      return mergedString.substring(0, mergedString.length()-2);   }       private static List getSquares(List numbers){      List squaresList = new ArrayList();              for(Integer number: numbers){         Integer square = new Integer(number.intValue() * number.intValue());                     if(!squaresList.contains(square)){            squaresList.add(square);         }      }      return squaresList;   }       private static int getMax(List numbers){      int max = numbers.get(0);              for(int i=1;i < numbers.size();i++){                 Integer number = numbers.get(i);                     if(number.intValue() > max){            max = number.intValue();         }      }      return max;   }       private static int getMin(List numbers){      int min = numbers.get(0);              for(int i=1;i < numbers.size();i++){         Integer number = numbers.get(i);                 if(number.intValue() < min){            min = number.intValue();         }      }      return min;   }       private static int getSum(List numbers){      int sum = (int)(numbers.get(0));              for(int i=1;i < numbers.size();i++){         sum += (int)numbers.get(i);      }      return sum;   }       private static int getAverage(List numbers){      return getSum(numbers) / numbers.size();   }}

实例

/*** java list 中的字符是否包括在另一个 list 中*/@Testvoid anyMatchTest() {    List permission = Arrays.asList("A", "B", "D");    List arr = Arrays.asList("C", "D", "E", "F");    boolean b = arr.stream().anyMatch(permission::contains);    System.out.println("" + b);}/*** 数组转Set\List*/void anyMatchTest() { String[] permsArr = "a,b,c".split(","); Set permsSet = Arrays.stream(permsArr).collect(Collectors.toSet());}