• 选中一部分代码，然后CTRL+ALT+T，可以在外面套上while循环,try..catch之类的
• 小案例：电影信息管理模块：用户可以上架、查询、下架、下架某个主演参演的电影

package Demo;import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;@Data
@AllArgsConstructor
@NoArgsConstructor
public class Movie {private String name;private double score;private String actor;private double price;
}

package Demo;import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;public class MovieService {private static List< Movie> movies = new ArrayList<>();private static Scanner sc = new Scanner(System.in);public void start() {while (true) {//选中一块区域，然后CTRL+ALT+TSystem.out.println("===电影信息操作系统===");System.out.println("1、上架");System.out.println("2、下架");System.out.println("3、查询某个电影");System.out.println("4、封杀某个明星");System.out.println("5、退出");System.out.println("请您输入操作命令：");int command = sc.nextInt();switch (command) {case 1:addMovie();break;case 2://removeMovie();break;case 3:searchMovie();break;case 4:banStar();break;case 5:System.out.println("退出成功！！");return;default:System.out.println("输入的命令有误！");}}}private void banStar() {System.out.println("====封杀明星====");System.out.println("请输入要封杀的明星：");String star = sc.next();for (int i = 0; i < movies.size(); i++) {Movie movie = movies.get(i);if (movie.getActor().contains(star)) {movies.remove(movie);System.out.println("封杀成功！");i--;}}}private void searchMovie() {System.out.println("====查询电影====");System.out.println("请输入要查询的电影名称：");String name = sc.next();Movie movie = searchMovieByName(name);if (movie != null) {System.out.println(movie);}else{System.out.println("没有找到该电影！");}}//根据电影名字查询电影对象返回public Movie searchMovieByName(String name) {for (Movie movie : movies) {if (movie.getName().equals(name)) {return movie;}}return null;}private void addMovie() {System.out.println("====上架电影====");//1、创建电影对象，封装这部电影信息Movie movie = new Movie();//2、给电影对象注入数据System.out.println("请输入电影名称：");movie.setName(sc.next());System.out.println("请输入电影评分：");movie.setScore(sc.nextDouble());System.out.println("请输入主演：");movie.setActor(sc.next());System.out.println("请输入价格：");movie.setPrice(sc.nextDouble());//3、将电影对象添加到集合中movies.add(movie);System.out.println("上架成功");}
}

package Demo;public class Test {public static void main(String[] args) {//1、创建电影对象：定义电影类//2、创建一个电影操作对象：专门负责对电影数据进行业务处理MovieService movieService = new MovieService();movieService.start();}
}

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• Map集合的三种遍历方式：

package Demo;import java.util.HashMap;
import java.util.Map;
import java.util.Set;public class MapTest {public static void main(String[] args) {Map<String,Integer> map = new HashMap<>();map.put("张三", 18);map.put("李四", 19);map.put("王五", 20);System.out.println(map);System.out.println("------------------");//1、将map集合的全部键放到set集合中Set<String> keys = map.keySet();for (String key : keys) {Integer value = map.get(key);System.out.println(key + "=" + value);}System.out.println("------------------");//2、把map集合转换成set集合，里面的元素类型都是键值对类型（Map.Entry<String,Integer>）Set<Map.Entry<String, Integer>> entries = map.entrySet();//快捷键：map.entrySet().var+回车for (Map.Entry<String, Integer> entry : entries) {//快捷键：entries.for+回车String key = entry.getKey();Integer value = entry.getValue();System.out.println(key + "=" + value);}System.out.println("------------------");//3、直接调用map集合的forEach方法遍历map.forEach((key,value)->{System.out.println(key + "=" + value);});}
}

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• Stream流
• 小案例：找到以“张”开头，并且是三个字的元素，存储到一个新集合

package Demo;import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;public class StreamDemo {public static void main(String[] args) {//找到以“张”开头，并且是三个字的元素，存储到一个新集合List<String> list = new ArrayList<>();list.add("张无忌");list.add("周芷若");list.add("赵敏");list.add("张强");list.add("张三丰");list.add("张小四");//法一：传统方法：找出姓张，名字三个字的，存入新集合中List<String> newList = new ArrayList<>();for (String name : list) {if (name.startsWith("张") && name.length() == 3) {newList.add(name);}}System.out.println(newList);System.out.println("-----------------");//法二：使用Stream流List<String> newList2 = list.stream().filter(name -> name.startsWith("张")).filter(name -> name.length() == 3).collect(Collectors.toList());System.out.println(newList2);}
}

• 获取Stream流的方式

package Demo;import java.util.*;
import java.util.stream.Stream;public class StreamDemo {public static void main(String[] args) {//获取Stream流的方式//1、获取集合的Stream流：调用集合提供的stream（）方法Collection<String> list = new ArrayList<>();Stream<String> s1 = list.stream();//快捷键:list.stream().var+回车//2、Map集合，怎么去拿Stream流Map<String,Integer> map = new HashMap<>();//获取键流Stream<String> s2 = map.keySet().stream();//获取值流Stream<Integer> s3 = map.values().stream();//获取键值对流Stream<Map.Entry<String,Integer>> s4 = map.entrySet().stream();//3、数组，获取数组的Stream流String[] arr = {"张三","李四","王五"};Stream<String> s5 = Arrays.stream(arr);Stream<String> s6 = Stream.of(arr);Stream<String> s7 = Stream.of("张三","李四","王五");}
}

• Stream提供的常用的中间方法，对流上的数据进行处理（返回新流，支持链式编程）

package Demo;import java.util.ArrayList;
import java.util.List;
import java.util.stream.Stream;public class StreamDemo {public static void main(String[] args) {//掌握Stream提供的常用的中间方法，对流上的数据进行处理（返回新流，支持链式编程）List<String> list = new ArrayList<>();list.add("张无忌");list.add("周芷若");list.add("赵敏");list.add("张强");list.add("张三丰");list.add("张小四");//1、过滤方法list.stream().filter(s -> s.startsWith("张")&&s.length()==3).forEach(s -> System.out.println(s));System.out.println("--------------------------------");//2、排序方法List<Double> scores = new ArrayList<>();scores.add(99.9);scores.add(66.6);scores.add(66.6);scores.add(77.7);scores.stream().sorted().forEach(s -> System.out.println(s));//默认升序System.out.println("--------------------------------");scores.stream().sorted((s1,s2) -> Double.compare(s2,s1)).forEach(s -> System.out.println(s));//降序System.out.println("--------------------------------");scores.stream().sorted((s1,s2) -> Double.compare(s2,s1)).limit(2).forEach(s -> System.out.println(s));//降序并且取前两个System.out.println("--------------------------------");scores.stream().sorted((s1,s2) -> Double.compare(s2,s1)).skip(2).forEach(s -> System.out.println(s));//降序并且跳过前两个System.out.println("--------------------------------");scores.stream().sorted((s1,s2) -> Double.compare(s2,s1)).distinct().forEach(s -> System.out.println(s));//去重System.out.println("--------------------------------");//映射/加工方法：把流上原来的数据拿出来变成新数据又放到流上去scores.stream().map(s -> "加十分后"+(s+10)).forEach(s -> System.out.println(s));System.out.println("--------------------------------");//合并流：Stream<String> s1 = Stream.of("张无忌", "周芷若", "赵敏", "张强", "张三丰", "张小四");Stream<Integer> s2 = Stream.of(1,2,3);Stream<Object> s3 = Stream.concat(s1, s2);System.out.println(s3.count());}
}

• Stream流的终结方法

package Demo;import java.util.*;
import java.util.stream.Collectors;public class StreamDemo {public static void main(String[] args) {List<Teacher> teachers = new ArrayList<>();teachers.add(new Teacher("张三", 18, 5000));teachers.add(new Teacher("李四", 19, 6000));teachers.add(new Teacher("王五", 20, 7000));teachers.stream().filter(t -> t.getSalary() > 5000).forEach(System.out::println);//遍历输出System.out.println("--------------------------------");long count = teachers.stream().filter(t -> t.getSalary() > 5000).count();//统计个数System.out.println(count);System.out.println("--------------------------------");Optional<Teacher> max = teachers.stream().max((t1, t2) -> Integer.compare(t1.getSalary(), t2.getSalary()));System.out.println(max.get());//获取最大值System.out.println("--------------------------------");Optional<Teacher> min = teachers.stream().min((t1, t2) -> Integer.compare(t1.getSalary(), t2.getSalary()));System.out.println(min.get());//获取最小值System.out.println("--------------------------------");List<String> list = new ArrayList<>();list.add("张无忌");list.add("周芷若");list.add("赵敏");list.add("张强");list.add("张三丰");list.add("张小四");//收集到list集合List<String> newList = list.stream().filter(s -> s.startsWith("张")).collect(Collectors.toList());//收集到set集合Set<String> newSet = list.stream().filter(s -> s.startsWith("张")).collect(Collectors.toSet());//收集到数组String[] newArray = list.stream().filter(s -> s.startsWith("张")).toArray(String[]::new);//toArray() 方法默认会返回 Object[] 类型的数组，而通过 String[]::new 可以直接得到 String[] 类型的数组//收集到map集合Map<String, Integer> newMap = list.stream().filter(s -> s.startsWith("张")).collect(Collectors.toMap(s -> s, s -> s.length()));}
}