Java JDK 1.8 lambda的用法详解

具体代码如下所示：

public class Student {
  private String id;
  private String name;
  private String age;
  private String address;
  public Student(String id, String name, String age, String address) {
    this.id = id;
    this.name = name;
    this.age = age;
    this.address = address;
  }
  public String getId() {
    return id;
  }
  public void setId(String id) {
    this.id = id;
  }
  public String getName() {
    return name;
  }
  public void setName(String name) {
    this.name = name;
  }
  public String getAge() {
    return age;
  }
  public void setAge(String age) {
    this.age = age;
  }
  public String getAddress() {
    return address;
  }
  public void setAddress(String address) {
    this.address = address;
  }
  @Override
  public String toString() {
    return "Student{" +
        "id='" + id + '\'' +
        ", name='" + name + '\'' +
        ", age='" + age + '\'' +
        ", address='" + address + '\'' +
        '}';
  }
}
public class TestStrean {
  public static void main(String[] args){
    Student stuA = new Student("1", "A", "M", "184");
    Student stuB = new Student("2", "B", "G", "163");
    Student stuC = new Student("3", "C", "M", "175");
    Student stuD = new Student("4", "D", "G", "158");
    Student stuE = new Student("5", "E", "M", "175");
    List<Student> list = new ArrayList<>();
    list.add(stuA);
    list.add(stuB);
    list.add(stuC);
    list.add(stuD);
    list.add(stuE);
    /*-----------forEach-----------------------*/
//    list.forEach(item -> item.setId(item.getAddress()+"test") );
    /*-----------filter-----------------------*/
//    List<Student> newList=list.stream().filter(item -> item.getAge().contains("G")).collect(Collectors.toList());
    /*-----------filter的复杂应用-----------------------*/
//    list.stream().filter(new Predicate<Student>(){
//
//      @Override
//      public boolean test(Student student) {
//        if(student.getName() !=null){
//          return student.getName().contains("30");
//        }else{
//          return true;
//        }
//      }
//    }).collect(Collectors.toList());
    /*-----------分页-----------------------*/
//    List<Student> newList=list.stream().skip(4).limit(3).collect(Collectors.toList());

    /*-----------map 返回一个新的list<Object>-----------------------*/
//    List<Student> newList=list.stream().map(item ->{
//      return new Student(
//          item.getAddress(),
//          item.getAge(),
//          item.getName(),
//          item.getId()
//      );
//    }).collect(Collectors.toList());
    /*-----------map 返回一个原来的的list<Student>并赋值-----------------------*/
//    List<Student> newList=list.stream().map(item ->{
//      item.setId("1");
//      return item;
//    }).collect(Collectors.toList());
    /*-----------flatMap-----------------------*/
//    List<Student> newList= list.stream().flatMap(item ->{
//      String[] split =item.getAddress().split("");
//      String[] s2 = (String[]) Arrays.stream(split).filter(s -> s.contains("1")).toArray();
//      return s2;
//        });
    /*-----------sorted compareTo排序-----------------------*/
//    List<Student> newList=list.stream().sorted((o1,o2)->{
//      if(o1.getAddress().equals(o2.getAddress())){
//        return Integer.parseInt(o1.getId())-Integer.parseInt(o2.getId());
//      }else{
//        return o1.getAddress().compareTo(o2.getAddress());
//      }
//    }).collect(Collectors.toList());
    /*-----------sorted Comparator排序-----------------------*/
//    List<Student> newList=list.stream().sorted(
//        Comparator.comparing(Student::getAddress).reversed()
//    ).collect(Collectors.toList());
    /*-----------sorted3 多条件排序-----------------------*/
//    List<Student> newList=list.stream().sorted(
//        Comparator.comparing(Student::getAddress).thenComparing(Comparator.comparing(Student::getId).reversed())
//    ).collect(Collectors.toList());
//    boolean b=list.stream().anyMatch(item -> item.getAge().contains("G"));
//    System.out.println(b);

    /*-----------Collector tomap----------------------*/
//    Map<String, String> newList=list.stream().sorted(
//        Comparator.comparing(Student::getAddress).thenComparing(Comparator.comparing(Student::getId).reversed())
//    ).collect(Collectors.toMap(Student::getId,Student::getAddress));

    /*-----------Collector groupingBy----------------------*/
    Map<String, List<Student>> ageMap = list.stream().collect(Collectors.groupingBy(Student::getAddress));
    System.out.println(ageMap );
  }
}

知识点扩展：

jdk 1.8 Lambda 表达式 遍历数组

Lambda 表达式可以把回调函数作为参数传递

常用的遍历数组的方式如下

  List<String> datas = new ArrayList<>();
  //遍历
  datas.forEach(item->{
   System.out.println(item);
  });

说明：

item就是每次遍历的当前元素

总结

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