JDK 8和JDK 17的区别和新特性大全

// JDK8
List<Integer> list = Arrays.asList(1, 2, 3, 4, 5);
list.forEach(n -> System.out.println(n));

// JDK17
List<Integer> list = Arrays.asList(1, 2, 3, 4, 5);
list.forEach((var n) -> System.out.println(n));

// JDK8
if (obj instanceof String) {
    String str = (String) obj;
    System.out.println(str.toUpperCase());
} else {
    System.out.println(obj);
}

// JDK17
if (obj instanceof String str) {
    System.out.println(str.toUpperCase());
} else {
    System.out.println(obj);
}

// JDK8
// 没有Java Flight Recorder库
// 没有ZGC垃圾回收器
// JDK17
// 使用Java Flight Recorder记录CPU时间
JFR.enable();
// 使用ZGC垃圾回收器
System.setProperty("jdk.garbageCollector", "Z");

// JDK8
List<Integer> list = Arrays.asList(1, 2, 3, 4, 5);
int sum = list.stream().filter(n -> n % 2 == 0).mapToInt(Integer::intValue).sum();

// JDK17
List<Integer> list = Arrays.asList(1, 2, 3, 4, 5);
List<Integer> evenList = list.stream().filter(n -> n % 2 == 0).toList();
Set<Integer> oddSet = list.stream().filter(n -> n % 2 != 0).toSet();

// JDK8
String dayOfWeek = "MON";
switch (dayOfWeek) {
    case "MON":
    case "TUE":
    case "WED":
    case "THU":
    case "FRI":
        System.out.println("Weekday");
        break;
    case "SAT":
    case "SUN":
        System.out.println("Weekend");
        break;
    default:
        System.out.println("Invalid day");
}

// JDK17
String dayOfWeek = "MON";
String dayType = switch (dayOfWeek) {
    case "MON", "TUE", "WED", "THU", "FRI" -> "Weekday";
    case "SAT", "SUN" -> "Weekend";
    default -> {
        System.out.println("Invalid day");
        yield "Invalid day";
    }
};

// JDK8
// 使用第三方HTTP库
// JDK17
HttpClient client = HttpClient.newHttpClient();
HttpRequest request = HttpRequest.newBuilder()
    .uri(URI.create("https://www.example.com/"))
    .build();
HttpResponse<String> response = client.send(request, HttpResponse.BodyHandlers.ofString());
System.out.println(response.body());