随手记录第十二话 -- JDK8-21版本的新增特性记录(Lambda,var,switch,instanceof,record,virtual虚拟线程等)

news2025/1/15 18:44:00

本文主要用于记录jdk8以来的新增特性及使用方法!

1.Java8 Lambda表达式(8)

1.1 方法引用

		List<String> list = List.of("1", "2", "3");
        list.forEach(i -> System.out.println(i));
        //方法引用
        list.forEach(System.out::println);

1.2 接口支持默认方法

public interface MyTest {
    
    default void defaultMethod(){
        System.out.println("default Method");
    }
}

1.3 Stream API流式API

		List<String> list = List.of("1", "2", "3");
        //过滤再循环
        list.stream().filter(i -> !"1".equals(i)).forEach(System.out::println);
        //过滤再输出
        List<String> list1 = list.stream().filter(i -> !"1".equals(i)).toList();
        System.out.println(JSONObject.toJSONString(list1)); //["2","3"]
        //过滤再转map
        List<Map<String, Object>> list2 = list.stream().filter(i -> !"1".equals(i)).map(s -> {
            Map<String, Object> map = new HashMap<>();
            map.put("a_" + s, s);
            return map;
        }).toList();
        System.out.println(JSONObject.toJSONString(list2)); //[{"a_2":"2"},{"a_3":"3"}]
        //转类型
        List<Long> list3 = list.stream().map(Long::valueOf).toList();
        System.out.println(JSONObject.toJSONString(list3)); //[1,2,3]

1.4 Map新增且实用的方法

		Map<String, Integer> map = new HashMap<>();
        map.put("a", 1);
        map.put("b", 2);
        //foreach
        map.forEach((key, value) -> System.out.println(key + ": " + value));
        //getOrDefault 取值为空返回默认值
        int c = map.getOrDefault("c", 22);
        System.out.println(c); //22
        //replace 如果存在值替换当前key的值
        map.replace("b", 10);
        System.out.println(map); //{a=1, b=10}
        //替换时带匹配值
        map.replace("b", 10, 20);
        System.out.println(map); //{a=1, b=20}
        //replaceAll 可对每个key或者value做操作
        map.replaceAll((key, value) -> value + 1);
        System.out.println(map); //{a=2, b=21}
        //putIfAbsent key不存在才存入
        map.putIfAbsent("a", 11);
        map.putIfAbsent("c", 3);
        System.out.println(map); //{a=2, b=21, c=3}
        //computeIfAbsent 如果值不存在 则执行后面的函数
        map.computeIfAbsent("d", key -> 4);
        System.out.println(map); //{a=2, b=21, c=3, d=4}
        //computeIfPresent 如果存在且值非空 可重新计算
        map.computeIfPresent("b", (key, value) -> value + 10);
        System.out.println(map); //{a=2, b=31, c=3, d=4}
        //compute 使用函数计算存入
        map.compute("b", (key, value) -> (value == null) ? 40 : value + 1);
        map.compute("e", (key, value) -> (value == null) ? 40 : value + 1);
        System.out.println(map); //{a=2, b=32, c=3, d=4, e=40}
        //merge
        map.merge("b", 1, (oldValue, newValue) -> oldValue + newValue);
        System.out.println(map); //{a=2, b=33, c=3, d=4, e=40}

        //remove 当指定key和值时才删除
        map.remove("a", 1);
        System.out.println(map); //{a=2, b=33, c=3, d=4, e=40}
        map.remove("a", 2);
        System.out.println(map); //{b=33, c=3, d=4, e=40}

        //of ofEntries 快捷创建 但映射不可变
        Map<String, Integer> of = Map.of("a", 1, "b", 2);
        System.out.println(of); //{b=2, a=1}
        Map<String, Integer> ofEntries = Map.ofEntries(
                Map.entry("a",1),
                Map.entry("b",2)
        );
        System.out.println(ofEntries); //{b=2, a=1}
//        of.put("a",3); //不管新增删除还是修改 俊辉报错

2. java11 var httpClient相关(11)

		var list = List.of("1", "2", "3");
        list.forEach((var e) -> System.out.println(e));

        String str = " ";
        System.out.println(str.isBlank()); //true
        System.out.println(str.isEmpty()); //false

		//java.net.http
        JSONObject object = new JSONObject();
        object.put("fromId", 11234);
        var httpClient = HttpClient.newBuilder().connectTimeout(Duration.ofSeconds(6)).build();
        HttpRequest httpRequest = HttpRequest.newBuilder(URI.create("http://192.168.168.199:9000/xxxxxx"))
        //post body请求
//                .setHeader("Content-Type","application/json; charset=utf-8")
//                .POST(HttpRequest.BodyPublishers.ofString(object.toJSONString()))
                .build();
        HttpResponse<String> httpResponse = httpClient.send(httpRequest, HttpResponse.BodyHandlers.ofString());
        System.out.println(httpResponse.body());


        //okhttp3 http请求
//        Request request = new Request.Builder()
//                .url(noticeUrl)
                .get()
//                .post(RequestBody.create(object.toJSONString(), MediaType.parse("application/json; charset=utf-8")))
//                .build();
//        Response response = Web3jUtils.httpClient.newCall(request).execute();
//        JSONObject jsonObject = JSONObject.parseObject(response.body().string());
//        log.warn("发现提现消息:{},{}", object.toJSONString(), jsonObject.toJSONString());

3.新表达式和模块匹配(12-15)

3.1 switch 多行文本 instanceof

		int day = 1;
        switch (day){
            case 2 -> System.out.println(false);
            case 1 -> System.out.println(true);
            default -> System.out.println("未知的!");
        }
		//多行文本
        String str = """
                text
                text
                """;

		//instanceof
        if(str instanceof String s1){
            System.out.println(s1.toUpperCase(Locale.ROOT));
        }

4.记录密封类虚拟线程(16-21)

记录

public record Point(int x, int y) {}

密封类

public abstract sealed class Shape permits Circle, Square {}
public final class Circle extends Shape {}
public final class Square extends Shape {}

虚拟线程

Thread.ofVirtual().start(() -> {
    System.out.println("Hello from virtual thread");
});

//使用Executors 创建和管理
ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor();
for (int i = 0; i < 10; i++) {
    executor.submit(() -> {
        System.out.println("Hello from virtual thread!");
    });
}
executor.shutdown();