Add more samples

Author: slateblua

content/posts/notes_on_jvm_anatomy.md

@@ -154,6 +154,161 @@ public class com/slateblua/bytecode/MyClass {
 }
 ```
 
+For a more "complex" example, let's create a toy-class InMemoryDataSource that extends AbstractDataSource
+and implements the LocalDataSource interface.
+
+```java
+package com.slateblua.bytecode;
+
+import java.util.List;
+
+public class InMemoryDataSource extends AbstractDataSource implements LocalDataSource {
+    static {
+        System.out.println("In-memory data source first accessed");
+    }
+
+    @Override
+    public List<String> getAllRecords () {
+        return List.of("Record", "Another record");
+    }
+
+    @Override
+    public String getRecordById (int key) {
+        return "Record " + key;
+    }
+
+    @Override
+    public void addRecord (String record) {
+        System.out.println("Record added: " + record);
+    }
+
+    @Override
+    public void deleteRecord (int key) {
+        System.out.println("Record deleted: " + key);
+    }
+}
+```
+
+The following bytecode is generated for the InMemoryDataSource class:
+
+```java
+// class version 62.0 (62)
+// access flags 0x21
+public class com/slateblua/bytecode/InMemoryDataSource extends com/slateblua/bytecode/AbstractDataSource implements com/slateblua/bytecode/LocalDataSource {
+
+  // compiled from: InMemoryDataSource.java
+  // access flags 0x19
+  public final static INNERCLASS java/lang/invoke/MethodHandles$Lookup java/lang/invoke/MethodHandles Lookup
+
+  // access flags 0x1
+  public <init>()V
+   L0
+    LINENUMBER 5 L0
+    ALOAD 0
+    INVOKESPECIAL com/slateblua/bytecode/AbstractDataSource.<init> ()V
+    RETURN
+   L1
+    LOCALVARIABLE this Lcom/slateblua/bytecode/InMemoryDataSource; L0 L1 0
+    MAXSTACK = 1
+    MAXLOCALS = 1
+
+  // access flags 0x1
+  // signature ()Ljava/util/List<Ljava/lang/String;>;
+  // declaration: java.util.List<java.lang.String> getAllRecords()
+  public getAllRecords()Ljava/util/List;
+   L0
+    LINENUMBER 12 L0
+    LDC "Record"
+    LDC "Another record"
+    INVOKESTATIC java/util/List.of (Ljava/lang/Object;Ljava/lang/Object;)Ljava/util/List; (itf)
+    ARETURN
+   L1
+    LOCALVARIABLE this Lcom/slateblua/bytecode/InMemoryDataSource; L0 L1 0
+    MAXSTACK = 2
+    MAXLOCALS = 1
+
+  // access flags 0x1
+  public getRecordById(I)Ljava/lang/String;
+   L0
+    LINENUMBER 17 L0
+    ILOAD 1
+    INVOKEDYNAMIC makeConcatWithConstants(I)Ljava/lang/String; [
+      // handle kind 0x6 : INVOKESTATIC
+      java/lang/invoke/StringConcatFactory.makeConcatWithConstants(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/String;[Ljava/lang/Object;)Ljava/lang/invoke/CallSite;
+      // arguments:
+      "Record \u0001"
+    ]
+    ARETURN
+   L1
+    LOCALVARIABLE this Lcom/slateblua/bytecode/InMemoryDataSource; L0 L1 0
+    LOCALVARIABLE key I L0 L1 1
+    MAXSTACK = 1
+    MAXLOCALS = 2
+
+  // access flags 0x1
+  public addRecord(Ljava/lang/String;)V
+   L0
+    LINENUMBER 22 L0
+    GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
+    ALOAD 1
+    INVOKEDYNAMIC makeConcatWithConstants(Ljava/lang/String;)Ljava/lang/String; [
+      // handle kind 0x6 : INVOKESTATIC
+      java/lang/invoke/StringConcatFactory.makeConcatWithConstants(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/String;[Ljava/lang/Object;)Ljava/lang/invoke/CallSite;
+      // arguments:
+      "Record added: \u0001"
+    ]
+    INVOKEVIRTUAL java/io/PrintStream.println (Ljava/lang/String;)V
+   L1
+    LINENUMBER 23 L1
+    RETURN
+   L2
+    LOCALVARIABLE this Lcom/slateblua/bytecode/InMemoryDataSource; L0 L2 0
+    LOCALVARIABLE record Ljava/lang/String; L0 L2 1
+    MAXSTACK = 2
+    MAXLOCALS = 2
+
+  // access flags 0x1
+  public deleteRecord(I)V
+   L0
+    LINENUMBER 27 L0
+    GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
+    ILOAD 1
+    INVOKEDYNAMIC makeConcatWithConstants(I)Ljava/lang/String; [
+      // handle kind 0x6 : INVOKESTATIC
+      java/lang/invoke/StringConcatFactory.makeConcatWithConstants(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/String;[Ljava/lang/Object;)Ljava/lang/invoke/CallSite;
+      // arguments:
+      "Record deleted: \u0001"
+    ]
+    INVOKEVIRTUAL java/io/PrintStream.println (Ljava/lang/String;)V
+   L1
+    LINENUMBER 28 L1
+    RETURN
+   L2
+    LOCALVARIABLE this Lcom/slateblua/bytecode/InMemoryDataSource; L0 L2 0
+    LOCALVARIABLE key I L0 L2 1
+    MAXSTACK = 2
+    MAXLOCALS = 2
+
+  // access flags 0x8
+  static <clinit>()V
+   L0
+    LINENUMBER 7 L0
+    GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
+    LDC "In-memory data source first accessed"
+    INVOKEVIRTUAL java/io/PrintStream.println (Ljava/lang/String;)V
+   L1
+    LINENUMBER 8 L1
+    RETURN
+    MAXSTACK = 2
+    MAXLOCALS = 0
+}
+```
+
+The <clinit> (the static initializer) method is called only once for a class. 
+It is called before any other method of the class can be executed. 
+
+In contrast, the <init> method is called for every object creation. Here it initializes the <init> method of the super class and the references to the current object.
+
 ### Execution engine: interpreters, JIT, AOT
 
 JVM may execute bytecode via