文章目录

1. 1. Java8总结

Java8总结

/**
 * Java8常见操作总结
 */
public class ExampleEmployee {

    private static List<Employee> employeeList = new ArrayList<>();

    static {
        employeeList.add(Employee.builder().name("zhangsan").salary(3000).office("beijing").build());
        employeeList.add(Employee.builder().name("lisi").salary(6000).office("shanghai").build());
        employeeList.add(Employee.builder().name("wangwu").salary(20000).office("guangzhou").build());
        employeeList.add(Employee.builder().name("zhaoliu").salary(8000).office("shenzhen").build());
        employeeList.add(Employee.builder().name("qiangqi").salary(8000).office("beijing").build());
        employeeList.add(Employee.builder().name("renba").salary(21000).office("beijing").build());
    }

    public static void main(String[] args) {
        // employeeList 是否包含 office="shanghai"
        boolean isMatch = employeeList.stream()
                .anyMatch(employee -> "shanghai".equals(employee.getOffice()));
        System.out.println(isMatch);
        System.out.println("-------------------------");

        // employeeList 的所有 salary 都大于4000
        boolean matched = employeeList.stream()
                .allMatch(employee -> employee.getSalary() > 4000);
        System.out.println(matched);
        System.out.println("-------------------------");

        // 工资最高
        Optional<Employee> hightSalary = employeeList.stream()
                .max((e1, e2) -> Integer.compare(e1.getSalary(), e2.getSalary()));
        System.out.println(hightSalary);
        System.out.println("-------------------------");

        Optional<Employee> hightSalary2 = employeeList.stream()
                .max(Comparator.comparingInt(Employee::getSalary));
        System.out.println(hightSalary2);
        System.out.println("-------------------------");

        // 返回姓名集合
        List<String> names = employeeList.stream()
                .map(Employee::getName)
                .collect(Collectors.toList());
        System.out.println(names);
        System.out.println("-------------------------");

        // List 转 Map
        Map<String, Employee> employeeMap = employeeList.stream()
                .collect(Collectors.toMap(Employee::getName, value -> value));
        employeeMap.forEach((key, value) -> {
            System.out.println(key + " : " + value);
        });
        System.out.println("-------------------------");

        // 统计 office 是 beijing 的个数
        long count = employeeList.stream()
                .filter(employee -> "beijing".equals(employee.getOffice()))
                .count();
        System.out.println(count);
        System.out.println("-------------------------");

        // List 转换为 Set
        Set<String> officeSet = employeeList.stream()
                .map(Employee::getOffice)
                .collect(Collectors.toSet());
        System.out.println(officeSet);
        System.out.println("-------------------------");

        // 查找 office 是 beijing 的员工
        Optional<Employee> allMatchedEmployees = employeeList.stream()
                .filter(employee -> "beijing".equals(employee.getOffice()))
                .findAny();
        System.out.println(allMatchedEmployees);
        System.out.println("-------------------------");

        // 按照工资的降序来列出员工信息
        List<Employee> descEmployeeList = employeeList.stream()
                .sorted((e1, e2) -> Integer.compare(e2.getSalary(), e1.getSalary()))
                .collect(Collectors.toList());
        System.out.println(descEmployeeList);
        System.out.println("-------------------------");

        // 按照名字的升序列出员工信息
        List<Employee> sortEmployeeByName = employeeList.stream()
                .sorted(Comparator.comparing(Employee::getName))
                .collect(Collectors.toList());
        System.out.println(sortEmployeeByName);
        System.out.println("-------------------------");

        // 获取工资最高的前两名员工信息
        List<Employee> top2EmployeeList = employeeList.stream()
                .sorted((e1, e2) -> Integer.compare(e2.getSalary(), e1.getSalary()))
                .limit(2)
                .collect(Collectors.toList());
        System.out.println(top2EmployeeList);
        System.out.println("-------------------------");

        // 获取平均工资
        OptionalDouble averageSalary = employeeList.stream()
                .mapToInt(Employee::getSalary)
                .average();
        System.out.println(averageSalary);
        System.out.println("-------------------------");

        // beijing 办公室平均工资
        OptionalDouble averageSalaryByOffice = employeeList.stream()
                .filter(employee -> "beijing".equals(employee.getOffice()))
                .mapToInt(Employee::getSalary)
                .average();
        System.out.println(averageSalaryByOffice);
        System.out.println("-------------------------");

        // Java8 分组操作
        Map<String, List<Employee>> groupMap = employeeList.stream()
                .collect(Collectors.groupingBy(Employee::getOffice));
        System.out.println(groupMap);
    }
}