JDK 14 新特性

2020年3月17日 JDK 14 发布，非 LTS 版本。

新特性: http://openjdk.java.net/projects/jdk/14/

• 305: Pattern Matching for instanceof (Preview)
• 343: Packaging Tool (Incubator)
• 345: NUMA-Aware Memory Allocation for G1
• 349: JFR Event Streaming
• 352: Non-Volatile Mapped Byte Buffers
• 358: Helpful NullPointerExceptions
• 359: Records (Preview)
• 361: Switch Expressions (Standard)
• 362: Deprecate the Solaris and SPARC Ports
• 363: Remove the Concurrent Mark Sweep (CMS) Garbage Collector
• 364: ZGC on macOS
• 365: ZGC on Windows
• 366: Deprecate the ParallelScavenge + SerialOld GC Combination
• 367: Remove the Pack200 Tools and API
• 368: Text Blocks (Second Preview)
• 370: Foreign-Memory Access API (Incubator)

中文

• 305: instanceof的模式匹配 (预览)
• 343: 打包工具 (Incubator)
• 345: G1的NUMA内存分配优化
• 349: JFR事件流
• 352: 非原子性的字节缓冲区映射
• 358: 友好的空指针异常
• 359: Records (预览)
• 361: Switch表达式扩展 (标准)
• 362: 弃用Solaris和SPARC端口
• 363: 移除CMS（Concurrent Mark Sweep）垃圾收集器
• 364: macOS系统上的ZGC
• 365: Windows系统上的ZGC
• 366: 弃用ParallelScavenge + SerialOld GC组合
• 367: 移除Pack200 Tools和API
• 368: 文本块 (第二个预览版)
• 370: 外部存储器API (Incubator)

if (o instanceof String) {
    String s = (String)o;
    ... use s ...
}

// New code
if (o instanceof String s) {
    ... use s ...
}

// instanceof 太多
static String formatter(Object o) {
    String formatted = "unknown";
    if (o instanceof Integer i) {
        formatted = String.format("int %d", i);
    } else if (o instanceof Long l) {
        formatted = String.format("long %d", l);
    } else if (o instanceof Double d) {
        formatted = String.format("double %f", d);
    } else if (o instanceof String s) {
        formatted = String.format("String %s", s);
    }
    return formatted;
}

// 用switch
static String formatterPatternSwitch(Object o) {
    return switch (o) {
        case Integer i -> String.format("int %d", i);
        case Long l    -> String.format("long %d", l);
        case Double d  -> String.format("double %f", d);
        case String s  -> String.format("String %s", s);
        default        -> o.toString();
    };
}

参考