java8 实现提取集合对象的每个属性

Java 8中提供了Stream API，可以通过该API实现快速高效的对集合对象的转换和处理。下面是提取集合对象的每个属性的完整攻略。

攻略步骤

1. 创建集合对象
   java
List<User> userList = new ArrayList<>();
2. 添加集合元素
   java
userList.add(new User("Tom", 20));
userList.add(new User("Lucy", 22));
userList.add(new User("Jerry", 25));
userList.add(new User("Andy", 23));
3. 提取集合对象的属性
   java
List<String> usernameList = userList.stream().map(User::getUsername).collect(Collectors.toList());
List<Integer> ageList = userList.stream().map(User::getAge).collect(Collectors.toList());
4. 获取属性结果
   java
System.out.println(usernameList);
System.out.println(ageList);
   输出结果为：
   [Tom, Lucy, Jerry, Andy]
[20, 22, 25, 23]

示例说明

示例1：提取用户列表中的用户名

public class User {
    private String username;
    private Integer age;

    public User(String username, Integer age) {
        this.username = username;
        this.age = age;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public Integer getAge() {
        return age;
    }

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

public class Main {
    public static void main(String[] args) {
        List<User> userList = new ArrayList<>();
        userList.add(new User("Tom", 20));
        userList.add(new User("Lucy", 22));
        userList.add(new User("Jerry", 25));
        userList.add(new User("Andy", 23));

        List<String> usernameList = userList.stream().map(User::getUsername).collect(Collectors.toList());
        System.out.println(usernameList);
    }
}

输出结果为：

[Tom, Lucy, Jerry, Andy]

示例2：提取用户列表中的年龄

public class User {
    private String username;
    private Integer age;

    public User(String username, Integer age) {
        this.username = username;
        this.age = age;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public Integer getAge() {
        return age;
    }

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

public class Main {
    public static void main(String[] args) {
        List<User> userList = new ArrayList<>();
        userList.add(new User("Tom", 20));
        userList.add(new User("Lucy", 22));
        userList.add(new User("Jerry", 25));
        userList.add(new User("Andy", 23));

        List<Integer> ageList = userList.stream().map(User::getAge).collect(Collectors.toList());
        System.out.println(ageList);
    }
}

输出结果为：

[20, 22, 25, 23]