JVM architecture, bytecode, class loading, heap and stack, garbage collector types, JIT compilation and common tuning flags.
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- What is the Java Virtual Machine (JVM)?
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Software that executes compiled Java bytecode, providing platform independence and runtime services like memory management- What does the javac tool do?
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Compiles Java source code (.java files) into platform-independent bytecode (.class files)- What is Java bytecode?
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Compiled intermediate code that is platform-independent and executed by the JVM, typically stored in .class files- Why is Java bytecode platform-independent?
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Bytecode is the same regardless of OS or CPU, and the JVM on each platform translates it to native machine code- Name the three phases of class loading
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Loading (read bytecode), linking (verify, prepare, resolve), initialization (execute static blocks)- What is the bootstrap class loader?
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Loads core Java classes from the JDK (java.lang, java.util, etc) from JAVA_HOME/lib- What is the application class loader?
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Loads user-defined classes and application classes from the classpath- What is bytecode verification?
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During class linking, the bytecode verifier checks for illegal operations, type mismatches, and security violations- What is the heap in JVM memory?
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Shared memory region where all objects are dynamically allocated, managed by the garbage collector- What is the stack in JVM memory?
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Per-thread memory region that stores method call frames containing local variables, primitive values, and object references- How is stack memory reclaimed?
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Automatically when a method returns and its frame is popped off the stack- What is StackOverflowError?
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Thrown when a thread exhausts its stack memory, typically from infinite recursion or very deep call stacks- What is OutOfMemoryError?
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Thrown when the heap is full and the garbage collector cannot free enough memory for a new object allocation- What is the young generation?
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Part of the heap where newly created objects are allocated, collected frequently by minor garbage collection- What is the old generation?
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Part of the heap where long-lived objects that survive young generation collections are promoted
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