Write Your Own Java Virtual Machine

The Java Virtual Machine is the cornerstone of the Java platform, but mainstream implementations such as OpenJDK are enormous and written in C++, so beginners easily lose their way in the code details. This book takes a different path: it neither interprets the specification documents nor analyzes the JDK source line by line. Instead, it starts from scratch in Go and builds, by hand, a Java virtual machine capable of running real class files. The book has 11 chapters, each layering new functionality onto the last: first a program skeleton built with the java command-line tool; then class-path searching and class-file parsing (magic number, version number, constant pool, attribute table); then the thread-private runtime data area (Java virtual machine stack, stack frames, local variable table, operand stack); then the instruction set and interpreter (including more than 150 bytecode instructions); and gradually support for classes and objects, method invocation and return, arrays and strings, class loading, and the method area. Chapter 9 discusses native method invocation and reflection, implementing basic methods such as Object.hashCode() and System.arraycopy(); Chapter 10 explains the exception-handling table and the athrow instruction; Chapter 11 traces the initialization of the System class and the execution of System.out.println(), bringing the book to a close. The code for each chapter can be compiled and run independently, so readers can work through it in order or skip around as needed.