InvokeVirtualCmd.java

package com.coderising.jvm.cmd;

import com.coderising.jvm.clz.ClassFile;
import com.coderising.jvm.constant.ConstantPool;
import com.coderising.jvm.constant.MethodRefInfo;
import com.coderising.jvm.engine.ExecutionResult;
import com.coderising.jvm.engine.JavaObject;
import com.coderising.jvm.engine.MethodArea;
import com.coderising.jvm.engine.StackFrame;
import com.coderising.jvm.method.Method;


public class InvokeVirtualCmd extends TwoOperandCmd {

	public InvokeVirtualCmd(ClassFile clzFile,String opCode) {
		super(clzFile,opCode);
	}

	@Override
	public String toString(ConstantPool pool) {
		
		return super.getOperandAsMethod(pool);
	}

	@Override
	public void execute(StackFrame frame,ExecutionResult result) {
		
		//先得到对该方法的描述
		MethodRefInfo methodRefInfo = (MethodRefInfo)this.getConstantInfo(this.getIndex());
		
		String className = methodRefInfo.getClassName();
		String methodName = methodRefInfo.getMethodName();
		
		// 我们没有实现System.out.println方法，  所以也不用建立新的栈帧， 直接调用Java的方法， 打印出来即可。 
		if(isSystemOutPrintlnMethod(className,methodName)){
			JavaObject jo = (JavaObject)frame.getOprandStack().pop();
			String value = jo.toString();
			System.err.println("-------------------"+value+"----------------");
			
			// 这里就是那个out对象， 因为是个假的，直接pop出来
			frame.getOprandStack().pop();
			
			return;
		}
		
		//注意：多态， 这才是真正的对象, 先从该对象的class 中去找对应的方法，找不到的话再去找父类的方法
		JavaObject jo = frame.getOprandStack().peek();
		
		MethodArea ma = MethodArea.getInstance();
		
		Method m = null;
		
		String currentClassName = jo.getClassName();
		
		while(currentClassName != null){
			
			ClassFile currentClassFile = ma.findClassFile(currentClassName);
			
			m = currentClassFile.getMethod(methodRefInfo.getMethodName(), 
					methodRefInfo.getParamAndReturnType());
			if(m != null){
				
				break;
				
			} else{
				//查找父类
				currentClassName = currentClassFile.getSuperClassName();
			}
		}	
		
		if(m == null){
			throw new RuntimeException("Can't find method for :" + methodRefInfo.toString());
		}
		
		
		result.setNextAction(ExecutionResult.PAUSE_AND_RUN_NEW_FRAME);
		
		result.setNextMethod(m);
	}

	private boolean isSystemOutPrintlnMethod(String className, String methodName) {
		return "java/io/PrintStream".equals(className) 
				&& "println".equals(methodName);
	}
	
	

}