InvokeVirtualCmd.java

package me.lzb.jvm.cmd;

import me.lzb.jvm.clz.ClassFile;
import me.lzb.jvm.constant.MethodRefInfo;
import me.lzb.jvm.engine.ExecutionResult;
import me.lzb.jvm.engine.JavaObject;
import me.lzb.jvm.engine.MethodArea;
import me.lzb.jvm.engine.StackFrame;
import me.lzb.jvm.method.Method;
import me.lzb.jvm.print.ExecutionVisitor;

public class InvokeVirtualCmd extends TwoOperandCmd {

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

    public String toString() {
        return super.getOperandAsMethod();
    }


    @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.out.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);
    }

    @Override
    public void printExecute(ExecutionVisitor visitor) {
        visitor.visitInvokeVirtualCmd(this);
    }

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