java8集合操作全集

1. List

   java8, 操作List对象(user对象)，把user对象的用户名字转为大写

   import java.util.ArrayList;
   import java.util.List;
   import java.util.stream.Collectors;public class UserNameConverter {public static void main(String[] args) {// 创建示例数据List<User> userList = new ArrayList<>();userList.add(new User(1L, "Alice", 25));userList.add(new User(2L, "Bob", 30));userList.add(new User(3L, "Charlie", 22));// 将用户名转换为大写List<User> convertedUsers = convertNamesToUpperCase(userList);// 输出结果convertedUsers.forEach(user -> System.out.println("用户 ID: " + user.getId() + ", 大写用户名: " + user.getName()));}public static List<User> convertNamesToUpperCase(List<User> userList) {return userList.stream().map(user -> {// 创建一个新的 User 对象，保持原始对象不变return new User(user.getId(),user.getName().toUpperCase(), // 将用户名转为大写user.getAge());}).collect(Collectors.toList());}
   }class User {private Long id;private String name;private Integer age;public User(Long id, String name, Integer age) {this.id = id;this.name = name;this.age = age;}// Getters 和 Setterspublic Long getId() { return id; }public String getName() { return name; }public Integer getAge() { return age; }
   }

   public static void convertNamesToUpperCaseInPlace(List<User> userList) {userList.forEach(user -> {user.setName(user.getName().toUpperCase()); // 直接修改原对象});
   }