https://axerzone.cn/categories/java%E5%9F%BA%E7%A1%80/Recent content in Java基础 on Weiming's BlogHugo -- gohugo.iozh-cn© 2026 WeimingThu, 18 Jan 2024 00:00:00 +0000https://axerzone.cn/posts/java-stream-api/Thu, 18 Jan 2024 00:00:00 +0000https://axerzone.cn/posts/java-stream-api/<h1 class="relative group">Stream API 用起来真香，但别乱用 <div id="stream-api-用起来真香但别乱用" class="anchor"></div> <span class="absolute top-0 w-6 transition-opacity opacity-0 -start-6 not-prose group-hover:opacity-100 select-none"> <a class="text-primary-300 dark:text-neutral-700 !no-underline" href="#stream-api-%e7%94%a8%e8%b5%b7%e6%9d%a5%e7%9c%9f%e9%a6%99%e4%bd%86%e5%88%ab%e4%b9%b1%e7%94%a8" aria-label="锚点">#</a> </span> </h1> <p>自从学了 Stream API，写 Java 的风格变了不少。以前过滤加转换要写十几行 for 循环，现在一行链式搞定，确实香。</p> <p>但用了一段时间也踩了不少坑，特别是并行流和性能方面，今天来聊聊。</p> <h2 class="relative group">基本操作过一遍 <div id="基本操作过一遍" class="anchor"></div> <span class="absolute top-0 w-6 transition-opacity opacity-0 -start-6 not-prose group-hover:opacity-100 select-none"> <a class="text-primary-300 dark:text-neutral-700 !no-underline" href="#%e5%9f%ba%e6%9c%ac%e6%93%8d%e4%bd%9c%e8%bf%87%e4%b8%80%e9%81%8d" aria-label="锚点">#</a> </span> </h2> <p>Stream 操作分两种：中间操作（返回新 Stream，可以链式调用）和终端操作（触发计算，产出结果）。</p>https://axerzone.cn/posts/java-reflection/Wed, 25 Oct 2023 00:00:00 +0000https://axerzone.cn/posts/java-reflection/<h1 class="relative group">反射慢？慢多少你测过吗 <div id="反射慢慢多少你测过吗" class="anchor"></div> <span class="absolute top-0 w-6 transition-opacity opacity-0 -start-6 not-prose group-hover:opacity-100 select-none"> <a class="text-primary-300 dark:text-neutral-700 !no-underline" href="#%e5%8f%8d%e5%b0%84%e6%85%a2%e6%85%a2%e5%a4%9a%e5%b0%91%e4%bd%a0%e6%b5%8b%e8%bf%87%e5%90%97" aria-label="锚点">#</a> </span> </h1> <p>&ldquo;反射很慢，尽量别用。&ldquo;这话你肯定听过。但到底慢多少？慢在哪？大部分人说不清楚，我之前也说不清楚，干脆自己测了一下。</p> <h2 class="relative group">怎么获取 Class 对象 <div id="怎么获取-class-对象" class="anchor"></div> <span class="absolute top-0 w-6 transition-opacity opacity-0 -start-6 not-prose group-hover:opacity-100 select-none"> <a class="text-primary-300 dark:text-neutral-700 !no-underline" href="#%e6%80%8e%e4%b9%88%e8%8e%b7%e5%8f%96-class-%e5%af%b9%e8%b1%a1" aria-label="锚点">#</a> </span> </h2> <p>反射的入口是 Class 对象，三种方式：</p>https://axerzone.cn/posts/java-generics/Sat, 12 Aug 2023 00:00:00 +0000https://axerzone.cn/posts/java-generics/<h1 class="relative group">Java 泛型这几个坑你肯定踩过 <div id="java-泛型这几个坑你肯定踩过" class="anchor"></div> <span class="absolute top-0 w-6 transition-opacity opacity-0 -start-6 not-prose group-hover:opacity-100 select-none"> <a class="text-primary-300 dark:text-neutral-700 !no-underline" href="#java-%e6%b3%9b%e5%9e%8b%e8%bf%99%e5%87%a0%e4%b8%aa%e5%9d%91%e4%bd%a0%e8%82%af%e5%ae%9a%e8%b8%a9%e8%bf%87" aria-label="锚点">#</a> </span> </h1> <p>Java 泛型这东西，看着简单用着顺手，直到踩坑才发现自己根本没搞懂。上周写作业一个泛型编译错误折腾了我一个多小时，气得把泛型重新学了一遍。</p> <h2 class="relative group">类型擦除到底擦了啥 <div id="类型擦除到底擦了啥" class="anchor"></div> <span class="absolute top-0 w-6 transition-opacity opacity-0 -start-6 not-prose group-hover:opacity-100 select-none"> <a class="text-primary-300 dark:text-neutral-700 !no-underline" href="#%e7%b1%bb%e5%9e%8b%e6%93%a6%e9%99%a4%e5%88%b0%e5%ba%95%e6%93%a6%e4%ba%86%e5%95%a5" aria-label="锚点">#</a> </span> </h2> <p>Java 的泛型是假泛型。编译之后泛型信息就没了，全变成 Object（或上界类型），这叫类型擦除。</p>https://axerzone.cn/posts/java-memory-model-volatile/Thu, 20 Jul 2023 00:00:00 +0000https://axerzone.cn/posts/java-memory-model-volatile/<h1 class="relative group">volatile 到底能保证什么 <div id="volatile-到底能保证什么" class="anchor"></div> <span class="absolute top-0 w-6 transition-opacity opacity-0 -start-6 not-prose group-hover:opacity-100 select-none"> <a class="text-primary-300 dark:text-neutral-700 !no-underline" href="#volatile-%e5%88%b0%e5%ba%95%e8%83%bd%e4%bf%9d%e8%af%81%e4%bb%80%e4%b9%88" aria-label="锚点">#</a> </span> </h1> <h2 class="relative group">Java 内存模型简单说 <div id="java-内存模型简单说" class="anchor"></div> <span class="absolute top-0 w-6 transition-opacity opacity-0 -start-6 not-prose group-hover:opacity-100 select-none"> <a class="text-primary-300 dark:text-neutral-700 !no-underline" href="#java-%e5%86%85%e5%ad%98%e6%a8%a1%e5%9e%8b%e7%ae%80%e5%8d%95%e8%af%b4" aria-label="锚点">#</a> </span> </h2> <p>聊 volatile 之前，得先说说 Java 内存模型（JMM）。放心，不讲太深，够理解 volatile 就行。</p>https://axerzone.cn/posts/jvm-gc/Mon, 08 May 2023 00:00:00 +0000https://axerzone.cn/posts/jvm-gc/<h1 class="relative group">JVM 垃圾回收看这篇就够了 <div id="jvm-垃圾回收看这篇就够了" class="anchor"></div> <span class="absolute top-0 w-6 transition-opacity opacity-0 -start-6 not-prose group-hover:opacity-100 select-none"> <a class="text-primary-300 dark:text-neutral-700 !no-underline" href="#jvm-%e5%9e%83%e5%9c%be%e5%9b%9e%e6%94%b6%e7%9c%8b%e8%bf%99%e7%af%87%e5%b0%b1%e5%a4%9f%e4%ba%86" aria-label="锚点">#</a> </span> </h1> <p>JVM 垃圾回收是面试八股文里的重头戏，也是我觉得最难啃的一块。概念多、算法多、收集器也多，第一次看的时候感觉脑子不够用。这篇把我学到的整理一下，尽量讲人话。</p> <p><figure><img class="my-0 rounded-md" loading="lazy" decoding="async" fetchpriority="low" alt="垃圾回收示意图" src="https://upload.wikimedia.org/wikipedia/commons/thumb/3/3c/Tracing-garbage-collection.svg/400px-Tracing-garbage-collection.svg.png" ></figure> </p> <h2 class="relative group">堆内存长什么样 <div id="堆内存长什么样" class="anchor"></div> <span class="absolute top-0 w-6 transition-opacity opacity-0 -start-6 not-prose group-hover:opacity-100 select-none"> <a class="text-primary-300 dark:text-neutral-700 !no-underline" href="#%e5%a0%86%e5%86%85%e5%ad%98%e9%95%bf%e4%bb%80%e4%b9%88%e6%a0%b7" aria-label="锚点">#</a> </span> </h2> <p>JVM 的堆分两大块：新生代（Young Generation）和老年代（Old Generation）。</p>https://axerzone.cn/posts/java-thread-pool/Fri, 10 Feb 2023 00:00:00 +0000https://axerzone.cn/posts/java-thread-pool/<h1 class="relative group">线程池这玩意，用不好真的会出事 <div id="线程池这玩意用不好真的会出事" class="anchor"></div> <span class="absolute top-0 w-6 transition-opacity opacity-0 -start-6 not-prose group-hover:opacity-100 select-none"> <a class="text-primary-300 dark:text-neutral-700 !no-underline" href="#%e7%ba%bf%e7%a8%8b%e6%b1%a0%e8%bf%99%e7%8e%a9%e6%84%8f%e7%94%a8%e4%b8%8d%e5%a5%bd%e7%9c%9f%e7%9a%84%e4%bc%9a%e5%87%ba%e4%ba%8b" aria-label="锚点">#</a> </span> </h1> <p>上周实验室项目出了个线上问题，排查了一下午发现是线程池配置不对导致的 OOM。这事让我意识到，线程池看着简单，用不好是真会出事的。</p> <h2 class="relative group">为什么要用线程池 <div id="为什么要用线程池" class="anchor"></div> <span class="absolute top-0 w-6 transition-opacity opacity-0 -start-6 not-prose group-hover:opacity-100 select-none"> <a class="text-primary-300 dark:text-neutral-700 !no-underline" href="#%e4%b8%ba%e4%bb%80%e4%b9%88%e8%a6%81%e7%94%a8%e7%ba%bf%e7%a8%8b%e6%b1%a0" aria-label="锚点">#</a> </span> </h2> <p>你可能觉得，new 一个 Thread 跑任务不就完了？能跑，但有几个问题：</p>https://axerzone.cn/posts/concurrenthashmap-deep-dive/Sun, 20 Nov 2022 00:00:00 +0000https://axerzone.cn/posts/concurrenthashmap-deep-dive/<h1 class="relative group">ConcurrentHashMap 到底怎么保证线程安全的 <div id="concurrenthashmap-到底怎么保证线程安全的" class="anchor"></div> <span class="absolute top-0 w-6 transition-opacity opacity-0 -start-6 not-prose group-hover:opacity-100 select-none"> <a class="text-primary-300 dark:text-neutral-700 !no-underline" href="#concurrenthashmap-%e5%88%b0%e5%ba%95%e6%80%8e%e4%b9%88%e4%bf%9d%e8%af%81%e7%ba%bf%e7%a8%8b%e5%ae%89%e5%85%a8%e7%9a%84" aria-label="锚点">#</a> </span> </h1> <p>上篇写了 HashMap，有同学私信问我 ConcurrentHashMap 和 HashMap 有什么区别。其实吧，区别大了去了，JDK8 的 ConcurrentHashMap 基本是重写的，跟 JDK7 完全两个思路。</p> <p>花了差不多一周把源码理清楚，这篇来聊聊它到底怎么在并发场景下保证线程安全。</p> <h2 class="relative group">JDK7 的 Segment 分段锁 <div id="jdk7-的-segment-分段锁" class="anchor"></div> <span class="absolute top-0 w-6 transition-opacity opacity-0 -start-6 not-prose group-hover:opacity-100 select-none"> <a class="text-primary-300 dark:text-neutral-700 !no-underline" href="#jdk7-%e7%9a%84-segment-%e5%88%86%e6%ae%b5%e9%94%81" aria-label="锚点">#</a> </span> </h2> <p>先说 JDK7 的方案，面试还是会问。</p>https://axerzone.cn/posts/hashmap-source-code/Thu, 15 Sep 2022 00:00:00 +0000https://axerzone.cn/posts/hashmap-source-code/<h1 class="relative group">HashMap 源码我读了三遍才看懂 <div id="hashmap-源码我读了三遍才看懂" class="anchor"></div> <span class="absolute top-0 w-6 transition-opacity opacity-0 -start-6 not-prose group-hover:opacity-100 select-none"> <a class="text-primary-300 dark:text-neutral-700 !no-underline" href="#hashmap-%e6%ba%90%e7%a0%81%e6%88%91%e8%af%bb%e4%ba%86%e4%b8%89%e9%81%8d%e6%89%8d%e7%9c%8b%e6%87%82" aria-label="锚点">#</a> </span> </h1> <p>大二下学期面试实习的时候，面试官问我 HashMap 的底层原理，我支支吾吾说了个&quot;数组加链表&quot;就说不下去了。回来之后就下定决心要把源码读一遍。结果读了三遍才算真正搞明白，这玩意比我想象的要精妙得多。</p> <p><figure><img class="my-0 rounded-md" loading="lazy" decoding="async" fetchpriority="low" alt="Hash Table 示意图" src="https://upload.wikimedia.org/wikipedia/commons/thumb/5/5e/Hash_table_5_0_1_1_1_1_0_SP.svg/380px-Hash_table_5_0_1_1_1_1_0_SP.svg.png" ></figure> </p> <h2 class="relative group">先说说 HashMap 的内部结构 <div id="先说说-hashmap-的内部结构" class="anchor"></div> <span class="absolute top-0 w-6 transition-opacity opacity-0 -start-6 not-prose group-hover:opacity-100 select-none"> <a class="text-primary-300 dark:text-neutral-700 !no-underline" href="#%e5%85%88%e8%af%b4%e8%af%b4-hashmap-%e7%9a%84%e5%86%85%e9%83%a8%e7%bb%93%e6%9e%84" aria-label="锚点">#</a> </span> </h2> <p>你打开 HashMap 的源码，会看到一个叫 <code>Node&lt;K,V&gt;[] table</code> 的数组。这就是 HashMap 的骨架。</p>