{
  "topic": "gc-jvm",
  "type": "single_choice",
  "schema_version": "1.0.0",
  "generated": "2026-09-02T00:00:00Z",
  "questions": [
    {
      "id": "sc-001",
      "type": "single_choice",
      "difficulty": 3,
      "tags": [
        "jvm",
        "gc",
        "heap"
      ],
      "question": "以下哪个不是 JVM 的 GC 类型？",
      "explanation": "三种主要 GC 类型是 Minor GC、Major GC 和 Full GC，没有 Super GC。",
      "source": null,
      "related": [],
      "options": {
        "A": "Minor GC",
        "B": "Major GC",
        "C": "Full GC",
        "D": "Super GC"
      },
      "answer": "D"
    },
    {
      "id": "sc-002",
      "type": "single_choice",
      "difficulty": 3,
      "tags": [
        "jvm",
        "gc",
        "heap"
      ],
      "question": "新生代通常使用哪种垃圾回收算法？",
      "explanation": "新生代使用复制算法（Copying），高效处理短生命周期对象。",
      "source": null,
      "related": [],
      "options": {
        "A": "标记-清除",
        "B": "标记-整理",
        "C": "复制算法",
        "D": "引用计数"
      },
      "answer": "C"
    },
    {
      "id": "sc-003",
      "type": "single_choice",
      "difficulty": 3,
      "tags": [
        "jvm",
        "gc",
        "heap"
      ],
      "question": "哪个垃圾收集器以低停顿为目标，并使用增量更新？",
      "explanation": "CMS（Concurrent Mark Sweep）以低停顿为目标，使用增量更新（Incremental Update）。",
      "source": null,
      "related": [],
      "options": {
        "A": "Serial",
        "B": "Parallel Scavenge",
        "C": "CMS",
        "D": "G1"
      },
      "answer": "C"
    },
    {
      "id": "sc-004",
      "type": "single_choice",
      "difficulty": 3,
      "tags": [
        "jvm",
        "gc",
        "heap"
      ],
      "question": "哪个垃圾收集器在 JDK 9 成为默认收集器，并支持停顿时间预测？",
      "explanation": "G1（Garbage First）在 JDK 9 成为默认收集器，支持可预测的停顿时间。",
      "source": null,
      "related": [],
      "options": {
        "A": "Serial",
        "B": "CMS",
        "C": "G1",
        "D": "ZGC"
      },
      "answer": "C"
    },
    {
      "id": "sc-005",
      "type": "single_choice",
      "difficulty": 3,
      "tags": [
        "jvm",
        "gc",
        "heap"
      ],
      "question": "ZGC 的设计目标是停顿时间低于______。",
      "explanation": "ZGC 设计目标是停顿时间低于 10ms，适合延迟敏感的应用。",
      "source": null,
      "related": [],
      "options": {
        "A": "100ms",
        "B": "50ms",
        "C": "10ms",
        "D": "1ms"
      },
      "answer": "C"
    },
    {
      "id": "sc-006",
      "type": "single_choice",
      "difficulty": 3,
      "tags": [
        "jvm",
        "gc",
        "heap"
      ],
      "question": "以下哪个属于 GC Root？",
      "explanation": "静态字段是 GC Root。其他 GC Root 还包括虚拟机栈局部变量、final static 常量、JNI 引用、synchronized 持有的对象。",
      "source": null,
      "related": [],
      "options": {
        "A": "堆中的局部变量",
        "B": "静态字段（static fields）",
        "C": "Eden 区中的对象",
        "D": "Survivor 区中的对象"
      },
      "answer": "B"
    },
    {
      "id": "sc-007",
      "type": "single_choice",
      "difficulty": 3,
      "tags": [
        "jvm",
        "gc",
        "heap"
      ],
      "question": "并发标记期间，当一个白色对象被黑色对象新增引用时，会产生什么问题？",
      "explanation": "这叫漏标（Missed Marking），存活对象可能因未被标记而被错误回收。",
      "source": null,
      "related": [],
      "options": {
        "A": "内存泄漏",
        "B": "漏标",
        "C": "栈溢出",
        "D": "死锁"
      },
      "answer": "B"
    },
    {
      "id": "sc-008",
      "type": "single_choice",
      "difficulty": 3,
      "tags": [
        "jvm",
        "gc",
        "heap"
      ],
      "question": "老年代使用哪种算法可以避免内存碎片，但 STW 时间更长？",
      "explanation": "标记-整理（Mark-Compact）通过移动对象消除碎片，但移动操作导致更长的 STW。",
      "source": null,
      "related": [],
      "options": {
        "A": "复制算法",
        "B": "标记-清除",
        "C": "标记-整理",
        "D": "引用计数"
      },
      "answer": "C"
    },
    {
      "id": "sc-009",
      "type": "single_choice",
      "difficulty": 3,
      "tags": [
        "jvm",
        "gc",
        "heap"
      ],
      "question": "哪个垃圾收集器支持 Mixed GC 并使用 SATB？",
      "explanation": "G1 支持 Mixed GC（同时收集新生代和老年代），并使用 SATB 进行并发标记。",
      "source": null,
      "related": [],
      "options": {
        "A": "Serial",
        "B": "CMS",
        "C": "G1",
        "D": "Parallel Scavenge"
      },
      "answer": "C"
    },
    {
      "id": "sc-010",
      "type": "single_choice",
      "difficulty": 3,
      "tags": [
        "jvm",
        "gc",
        "heap"
      ],
      "question": "CMS 的初始标记（Initial Mark）阶段做什么？",
      "explanation": "CMS 初始标记阶段（需要 STW）枚举 GC Roots 的直接引用，标记为灰色，建立起始快照。",
      "source": null,
      "related": [],
      "options": {
        "A": "回收所有垃圾",
        "B": "枚举 GC Roots 直接引用并标记为灰色",
        "C": "移动对象以压缩内存",
        "D": "清除不可达对象"
      },
      "answer": "B"
    }
  ]
}