Building a Java Interpreter

1. Building a Java Interpreter CS 142 (b) 01/14

2. Lab Sessions • Monday, Wednesday • 10am – noon • ICS 189 • Send an email or make an appointment with the TA

3. Java Interpreter • Input: a bytecode instruction stream • Output: a native-code instruction stream • In our project: • Translate each bytecode instruction to C++ code

4. Instructions We Are Interested in • iconst, iload and istore • iadd • if_icmpne, if_icmpeq, if_icmpgt, if_icmplt, ifeq, ifne, ifgt, iflt • goto • invokestatic • return

5. Building an Interpreter void interpret(InstructionSeq is){ for (Instruction i = is.first(); i != null; i = next) { intopCode = i.getOpCode(); next = is.nextInstruction(i); switch(opCode){ case iload: int index = i.getOperand(); int value = values.get(index); push(value); break; case istore: int index = i.getOperand(); int value = pop(); values.set(index, value); break; } }

6. Building an Interpreter (Cond.) for(Instruction i = is.first(); i != null; i = next){ intopCode = i.getOpCode(); next = is.nextInstruction(i); switch(opCode){ case iadd: int value1 = pop(); int value2 = pop(); push(value1 + value2); break; case if_icmpeq: int value1 = pop(); int value2 = pop(); int target = i.getOperand(); if(value1 == value2) next = is.getInstruction(target); break; case goto: int target = i.getOperand(); next = is.getInstruction(target); break; }

7. Building an Interpreter (Cond.) void interpret(InstructionSeqis){ for(Instruction i = is.first(); i != null; i = next){ … case invokestatic: String mName = ((CallInsruction) i). getTarget(); InstructionSetnewSet = findInstructionSetforMethod(mName); invoke(newSet); break; } }

8. Handling of println • If the target of a static method is System.out.println, just call C++ function printf on the parameter string