StreamAPI在Java8版本中使用，關注的是對數據的篩選、查找、存儲等

它可以做的事情有：過濾、排序、映射、歸約

Stream實例化中間操作（過濾、排序、映射、規約）終止操作（匹配查找、歸約、收集）

public class EmployeeData { public static List<Employee> getEmployees(){ List<Employee> list = new ArrayList<>(); list.add(new Employee(1001, '馬化騰', 34, 6000.38)); list.add(new Employee(1002, '馬云', 12, 9876.12)); list.add(new Employee(1003, '劉強東', 33, 3000.82)); list.add(new Employee(1004, '雷軍', 26, 7657.37)); list.add(new Employee(1005, '李彥宏', 65, 5555.32)); list.add(new Employee(1006, '比爾蓋茨', 42, 9500.43)); list.add(new Employee(1007, '任正非', 26, 4333.32)); list.add(new Employee(1008, '扎克伯格', 35, 2500.32)); return list; } }

package JDK_8;import org.junit.Test;import java.util.Arrays;import java.util.List;import java.util.Optional;import java.util.stream.Collectors;import java.util.stream.Stream;public class StreamAPI { // 方式1：使用集合創建Stream @Test public void test1() {List<Employee> list = EmployeeData.getEmployees();// 返回一個順序流Stream<Employee> stream = list.stream();// 返回一個并行流Stream<Employee> employeeStream = list.parallelStream(); } // 方式2：使用數組創建流對象 @Test public void test2() {Employee e1 = new Employee(1003, 'WZY', 26, 3000.69);Employee e2 = new Employee(1007, '王紫玉', 25, 8888);Employee[] list2 = new Employee[]{e1, e2};Stream<Employee> stream = Arrays.stream(list2);stream.forEach(System.out::println); } // 通過Stream.of 創建 @Test public void test3() {Stream<Integer> stream = Stream.of(1, 2, 3, 4, 5, 6);stream.forEach(System.out::println); } // Stream.filter進行過濾 @Test public void test4() {List<Employee> list = EmployeeData.getEmployees();list.stream().filter(employee -> employee.getAge() > 25).forEach(System.out::println); } // 使用StreamAPI篩選 @Test public void test5() {List<Employee> list = EmployeeData.getEmployees();list.add(new Employee(1004, 'wzy', 25, 18888));list.add(new Employee(1004, 'wzy', 25, 18888));list.add(new Employee(1004, 'wzy', 25, 18888));list.add(new Employee(1004, 'wzy', 25, 18888));list.stream().forEach(System.out::println);System.out.println();list.stream().distinct().forEach(System.out::println); } @Test public void test6() {List<String> list = Arrays.asList('a', 'b', 'c');//map(Function<? super T,? extends R> mapper)//返回由給定函數應用于此流的元素的結果組成的流。list.stream().map(s -> s.toUpperCase()).forEach(System.out::println); } // 使用StreamAPI篩選：工資大于6000的員工 @Test public void test7() {List<Employee> list = EmployeeData.getEmployees();list.stream().filter(s -> s.getSalary() > 6000).forEach(System.out::println); } // StreamAPI映射：map,接收參數，將參數轉換為其他形式的信息； @Test public void test8() {List<Employee> list = EmployeeData.getEmployees();list.stream().map(e -> e.getAge()).forEach(System.out::println); } // StreamAPI排序,sorted幫助實現Comparable接口進行對象比較 @Test public void test9() {List<Employee> list = EmployeeData.getEmployees();list.stream().sorted((e1, e2) -> { int ageValue = Integer.compare(e1.getAge(), e2.getAge()); if (ageValue != 0) {return ageValue; } else {return Double.compare(e1.getSalary(), e2.getSalary()); }}).forEach(System.out::println); } // StreamAPI匹配:所有元素是否滿足下列條件 @Test public void test10() {List<Employee> list = EmployeeData.getEmployees();boolean allMatch = list.stream().allMatch(e -> e.getSalary() > 5000);System.out.println(allMatch); } // StreamAPI查找：返回第一個元素 @Test public void test11() {List<Employee> list = EmployeeData.getEmployees();Optional<Employee> first = list.stream().findFirst();System.out.println(first); } // StreamAPI查找：返回薪水數最大的員工 @Test public void test12() {List<Employee> list = EmployeeData.getEmployees();Stream<Double> salaryStream = list.stream().map(e -> e.getSalary());Optional<Double> max = salaryStream.max(Double::compare);System.out.println(max); } // StreamAPI查找：薪水最小的員工對像 @Test public void test13() {List<Employee> list = EmployeeData.getEmployees();Optional<Employee> min = list.stream().min((e1, e2) -> Double.compare(e1.getSalary(), e2.getSalary()));System.out.println(min); } // StreamAPI:歸約 @Test public void test14() {List<Employee> list = EmployeeData.getEmployees();Stream<Double> salaryStream = list.stream().map(e -> e.getSalary());Optional<Double> sum = salaryStream.reduce((s1, s2) -> s1 + s2);System.out.println(sum.get()); } // StreamAPI：收集 @Test public void test15(){List<Employee> list = EmployeeData.getEmployees();List<Employee> employeeList = list.stream().filter(e -> e.getSalary() > 5000).collect(Collectors.toList());for (Employee employee : employeeList) { System.out.println(employee);} }}

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