Stream的终止操作

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匹配与查找

1 - 匹配与查找 // 1 - 匹配与查找 @Test public void test0(){ List<Employee> employeeList = EmployeeData.getEmployees(); //allMatch(Predicate p) --- 检查是否匹配所有元素。 // 练习:是否所有的员工的年龄都大于18 boolean allMatch = employeeList.stream().allMatch(e -> e.getAge() > 18); System.out.println(allMatch); //anyMatch(Predicate p) --- 检查是否至少匹配一个元素。 // 练习:是否存在员工的工资大于10000 boolean anyMatch = employeeList.stream().anyMatch(e -> e.getSalary() > 10000); System.out.println(anyMatch); //noneMatch(Predicate p) --- 检查是否没有匹配的元素。 // 练习: 是否存在员工姓"雷" boolean noneMatch = employeeList.stream().noneMatch(e -> e.getName().startsWith("雷")); System.out.println(noneMatch); //findFirst --- 返回第一个元素 Optional<Employee> first = employeeList.stream().findFirst(); System.out.println(first); //findAny --- 返回当前流中的任意元素 Optional<Employee> any = employeeList.stream().findAny(); System.out.println(any); } @Test public void test1(){ List<Employee> employeeList = EmployeeData.getEmployees(); //count --- 返回流中元素的总个数 long count = employeeList.stream().count(); System.out.println(count); //max(Comparator c) --- 返回流中最大值 // 练习: 返回最高的工资 Stream<Double> money = employeeList.stream().map(e1 -> e1.getSalary()); Optional<Double> maxMoney = money.max(Double::compareTo); System.out.println(maxMoney); //min(Comparator c) --- 返回流中最小值 // 练习: 返回最低工资的员工 Optional<Employee> employee = employeeList.stream().min((e1, e2) -> Double.compare(e1.getSalary(), e2.getSalary())); System.out.println(employee); //forEach(Consumer c) --- 内部迭代 employeeList.stream().forEach(System.out::println); //使用集合的遍历操作方法 employeeList.forEach(System.out::println); }

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归约

2 - 归约 // 2 - 归约 @Test public void test2(){ //reduce(T identity,BinaryOperator b) --- 可以将流中元素反复结合起来，得到一个值。返回T //练习1: 计算1-10的自然数的和 List<Integer> list = Arrays.asList(1,2,3,4,5,6,7,8,9,10); Integer reduce = list.stream().reduce(0, Integer::sum); System.out.println(reduce); //reduce(BinaryOperator b) --- 可以将流中元素反复结合起来，得到一个值。返回 Optional<T> //练习2: 计算公司所有员工工资的综合 List<Employee> employeeList = EmployeeData.getEmployees(); // Optional<Double> reduce1 = employeeList.stream().map(e1 -> e1.getSalary()).reduce(Double::sum); Optional<Double> reduce1 = employeeList.stream().map(e1 -> e1.getSalary()).reduce((d1,d2) -> d1 + d2); System.out.println(reduce1); }

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收集

3 - 收集 // 3 - 收集 @Test public void test3(){ //collect(Collection c) --- 将流转换为其他形式。接受一个Collector接口的实现，用于给Stream中元素做汇总的方法 //练习1: 查找工资大于6000的员工 结果返回为一个List或Set List<Employee> employees = EmployeeData.getEmployees(); List<Employee> employeeList = employees.stream().filter(e -> e.getSalary() > 6000).collect(Collectors.toList()); employeeList.forEach(System.out::println); System.out.println(); Set<Employee> employeeSet = employees.stream().filter(e -> e.getSalary() > 6000).collect(Collectors.toSet()); employeeSet.forEach(System.out::println); }