JDK1.8--体验Stream表达式，从一个对象集合中获取每一个对象的某一个值返回新集合

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开发工具eclipse

```java
package com.echo.demo;

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

public class GetStreamLong {

public static void main(String[] args) {

A a = new A();
a.setId(1);
a.setAge(22);
a.setName("a");

A a1 = new A();
a1.setId(2);
a1.setAge(22);
a1.setName("a1");

A a2 = new A();
a2.setId(3);
a2.setAge(22);
a2.setName("a2");

A a3 = new A();
a3.setId(4);
a3.setAge(22);
a3.setName("a3");

List<A> list = new ArrayList<>();
list.add(a3);
list.add(a2);
list.add(a1);
list.add(a);

List<Integer> list1 = list.stream().map(A::getId).collect(Collectors.toList());
List<Integer> list2 = list.stream().map(A::getAge).collect(Collectors.toList());//未去重
List<Integer> list3 = list.stream().map(A::getAge).distinct().collect(Collectors.toList());//已去重
System.out.println(list1);
System.out.println(list2);
System.out.println(list3);
}

static class A{
private Integer id;
private Integer age;
private String name;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}

}

```

返回结果