Java8 flatMap demo 代码直接可以运行

参考自:http://www.cnblogs.com/shenlanzhizun/p/6027042.html

package com.by.interfaces;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

class Student {

public Student(long id, String name, int age, int grade, String major, String school) {
this.id = id;
this.name = name;
this.age = age;
this.grade = grade;
this.major = major;
this.school = school;
}

public Student(String name) {
this.name = name;
}

public Student() {
}

private List<String> attributes = Arrays.asList("111", "222", "333");

/**
* 学号
*/
private long id;

private String name;

private int age;

/**
* 年级
*/
private int grade;

/**
* 专业
*/
private String major;

/**
* 学校
*/
private String school;

public long getId() {
return id;
}

public void setId(long id) {
this.id = id;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public int getAge() {
return age;
}

public void setAge(int age) {
this.age = age;
}

public int getGrade() {
return grade;
}

public void setGrade(int grade) {
this.grade = grade;
}

public String getMajor() {
return major;
}

public void setMajor(String major) {
this.major = major;
}

public String getSchool() {
return school;
}

public void setSchool(String school) {
this.school = school;
}

public List<String> getAttributes() {
return attributes;
}

public void setAttributes(List<String> attributes) {
this.attributes = attributes;
}
}

public class Main {
public static void main(String[] args) {

List<Student> students = new ArrayList<Student>();

students.add(new Student(20160001, "孔明4", 20, 1, "土木工程", "武汉大学"));
students.add(new Student(20160002, "伯约", 21, 2, "信息安全", "武汉大学"));
students.add(new Student(20160003, "玄德", 22, 3, "经济管理", "武汉大学"));
students.add(new Student(20160004, "云长", 21, 2, "信息安全", "武汉大学"));
students.add(new Student(20161001, "翼德", 21, 2, "机械与自动化", "华中科技大学"));
students.add(new Student(20161002, "元直", 23, 4, "土木工程", "华中科技大学"));
students.add(new Student(20161003, "奉孝", 23, 4, "计算机科学", "华中科技大学"));
students.add(new Student(20162001, "仲谋", 22, 3, "土木工程", "浙江大学"));
students.add(new Student(20162002, "鲁肃", 23, 4, "计算机科学", "浙江大学"));
students.add(new Student(20163001, "丁奉", 24, 5, "土木工程", "南京大学"));

//mapToLong的使用demo
double value = students.stream().filter(student -> "计算机科学".equals(student.getMajor())).mapToLong(aaa -> aaa.getId()).sum();

String[] strs = {"java8", "is", "easy", "to", "use"};

List<String[]> distinctStrs = Arrays.stream(strs)
.map(str -> str.split(""))  // 映射成为Stream<String[]>
.distinct()
.collect(Collectors.toList());

distinctStrs.forEach(strings -> Arrays.stream(strings).forEach(s -> System.out.println(s)));

System.out.println("==================================map方式");

List<String> distinctStrsByFlatMap = Arrays.stream(strs)
.map(str -> str.split(""))  // 映射成为Stream<String[]>
.flatMap(Arrays::stream)  // 扁平化为Stream<String>
.distinct()
.collect(Collectors.toList());

distinctStrsByFlatMap.forEach(s -> System.out.println(s));

System.out.println("==================================flatMap的方式");

List<List<Student>> studentss = new ArrayList<>();
studentss.add(students);
studentss.add(students);
System.out.println(studentss.size());

System.out.println("经过了flatmap处理后的stream查看下尺寸是多少" + studentss.stream().flatMap(students1 -> students1.stream()).count());

System.out.println(studentss.stream().flatMap(students1 -> students1.stream()).max((o1, o2) -> (o1.getName().length() - o2.getName().length())).get().getName());

System.out.println("经过了flatMap进行了彻底的流处理查看下有多少流" + studentss.stream().flatMap(students1 -> students1.stream()).flatMap(student -> student.getAttributes().stream()).count());

studentss.stream().flatMap(students1 -> students1.stream()).flatMap(student -> student.getAttributes().stream()).forEach(s -> System.out.println(s));

}
}