stackframe.java

这是有关Java虚拟机的实现代码,是学习和使用Java虚拟机的朋友们不可或缺的代码

/*
* Copyright (c) 1996-1999 Bill Venners. All Rights Reserved.
*
* This Java source file is part of the Interactive Illustrations Web
* Site, which is delivered in the applets directory of the CD-ROM
* that accompanies the book "Inside the Java 2 Virtual Machine" by Bill
* Venners, published by McGraw-Hill, 1999, ISBN: 0-07-135093-4. This
* source file is provided for evaluation purposes only, but you can
* redistribute it under certain conditions, described in the full
* copyright notice below.
*
* Full Copyright Notice:
*
* All the web pages and Java applets delivered in the applets
* directory of the CD-ROM, consisting of ".html," ".gif," ".class,"
* and ".java" files, are copyrighted (c) 1996-1999 by Bill
* Venners, and all rights are reserved.  This material may be copied
* and placed on any commercial or non-commercial web server on any
* network (including the internet) provided that the following
* guidelines are followed:
*
* a. All the web pages and Java Applets (".html," ".gif," ".class,"
* and ".java" files), including the source code, that are delivered
* in the applets directory of the CD-ROM that
* accompanies the book must be published together on the same web
* site.
*
* b. All the web pages and Java Applets (".html," ".gif," ".class,"
* and ".java" files) must be published "as is" and may not be altered
* in any way.
*
* c. All use and access to this web site must be free, and no fees
* can be charged to view these materials, unless express written
* permission is obtained from Bill Venners.
*
* d. The web pages and Java Applets may not be distributed on any
* media, other than a web server on a network, and may not accompany
* any book or publication.
*
* BILL VENNERS MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE
* SUITABILITY OF THE SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING
* BUT NOT LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR PARTICULAR PURPOSE, OR NON-INFRINGEMENT.  BILL VENNERS
* SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED BY A LICENSEE AS A
* RESULT OF USING, MODIFYING OR DISTRIBUTING THIS SOFTWARE OR ITS
* DERIVATIVES.
*/
package COM.artima.jvmsim;

/**
* This class represents the stack frame of the executing
* method.
*
* @author  Bill Venners
*/
class StackFrame {

    // optop is pointer to top of operand stack. Always points
    // to next location.
    private int optop = 0;
    private Object[] operandStack;

    private Object[] localVars;

    StackFrame(int maxStack, int maxLocals) {
        if (maxStack > 65535 || maxLocals > 65535) {
            throw new JVMSimError("maxStack = " + maxStack
             + "maxLocals = " + maxLocals);
        }
        operandStack = new Object[maxStack];
        localVars = new Object[maxLocals];
    }

    void resetState() {
        optop = 0;
        for (int i = 0; i < operandStack.length; ++i) {
            operandStack[i] = null;
        }
        for (int i = 0; i < localVars.length; ++i) {
            localVars[i] = null;
        }
    }

    int getOptop() {
        return optop;
    }

    Object[] getOperandStack() {
        return operandStack;
    }

    Object[] getLocalVars() {
        return localVars;
    }

    void setLocalDouble(int i, double theDouble) {
        if (i + 1 >= localVars.length) { // use i + 1 because doubles take two
            throw new JVMSimError();
        }
        localVars[i] = new Double(theDouble);
        localVars[i + 1] = null;
    }

    void setLocalFloat(int i, float val) {
        if (i >= localVars.length) {
            throw new JVMSimError();
        }
        localVars[i] = new Float(val);
    }

    void setLocalInt(int i, int val) {
        if (i >= localVars.length) {
            throw new JVMSimError();
        }
        localVars[i] = new Integer(val);
    }

    void setLocalLong(int i, long theLong) {
        if (i + 1 >= localVars.length) { // use i + 1 because longs take two
            throw new JVMSimError();
        }
        localVars[i] = new Long(theLong);
        localVars[i + 1] = null;
    }

    void setLocalObject(int i, Object val) {
        if (i >= localVars.length) {
            throw new JVMSimError();
        }
        localVars[i] = val;
    }

    double getLocalDouble(int i) { // untested
        if (i >= localVars.length) {
            throw new JVMSimError();
        }
        return ((Double) localVars[i]).doubleValue();
    }

    float getLocalFloat(int i) {
        if (i >= localVars.length) {
            throw new JVMSimError();
        }
        return ((Float) localVars[i]).floatValue();
    }

    int getLocalInt(int i) {
        if (i >= localVars.length) {
            throw new JVMSimError();
        }
        return ((Integer) localVars[i]).intValue();
    }

    long getLocalLong(int i) { // untested
        if (i >= localVars.length) {
            throw new JVMSimError();
        }
        return ((Long) localVars[i]).longValue();
    }

    Object getLocalObject(int i) {
        if (i >= localVars.length) {
            throw new JVMSimError();
        }
        return localVars[i];
    }

    void pushDouble(double theDouble) { // untested
        if (optop >= operandStack.length) {
            throw new JVMSimError("optop = " + optop);
        }
        operandStack[optop] = new Double(theDouble);
        operandStack[optop + 1] = null;
        optop += 2; // A double occupies two words on the stack
    }

    void pushFloat(float f) {
        if (optop >= operandStack.length) {
            throw new JVMSimError("optop = " + optop);
        }
        operandStack[optop] = new Float(f);
        ++optop;
    }

    void pushInt(int val) {
        if (optop >= operandStack.length) {
            throw new JVMSimError("optop = " + optop);
        }
        operandStack[optop] = new Integer(val);
        ++optop;
    }

    void pushLong(long theLong) { // untested
        if (optop >= operandStack.length) {
            throw new JVMSimError("optop = " + optop);
        }
        operandStack[optop] = new Long(theLong);
        operandStack[optop + 1] = null;
        optop += 2; // A long occupies two words on the stack
    }

    void pushObject(Object theObject) {
        if (optop >= operandStack.length) {
            throw new JVMSimError("optop = " + optop);
        }
        operandStack[optop] = theObject;
        ++optop;
    }

    void pushReturnAddress(ReturnAddress retAddr) {
        if (optop >= operandStack.length) {
            throw new JVMSimError("optop = " + optop);
        }
        operandStack[optop] = retAddr;
        ++optop;
    }

    double popDouble() {
        if (optop <= 1) { // Use 1 because double occupies two slots
            throw new JVMSimError();
        }
        optop -= 2;
        double theDouble = ((Double) operandStack[optop]).doubleValue();
        operandStack[optop] = null; // make available for gc
        return theDouble;
    }

    float popFloat() {
        if (optop <= 0) {
            throw new JVMSimError();
        }
        --optop;
        float f = ((Float) operandStack[optop]).floatValue();
        operandStack[optop] = null; // make available for gc
        return f;
    }

    int popInt() {
        if (optop <= 0) {
            throw new JVMSimError();
        }
        --optop;
        int val = ((Integer) operandStack[optop]).intValue();
        operandStack[optop] = null; // make available for gc
        return val;
    }

    long popLong() {
        if (optop <= 1) { // Use 1 because long occupies two slots
            throw new JVMSimError();
        }
        optop -= 2;
        long theLong = ((Long) operandStack[optop]).longValue();
        operandStack[optop] = null; // make available for gc
        return theLong;
    }

    Object popObject() {
        if (optop <= 0) {
            throw new JVMSimError();
        }
        --optop;
        Object theObject = operandStack[optop];
        operandStack[optop] = null; // make available for gc
        return theObject;
    }

    ReturnAddress popReturnAddress() {
        if (optop <= 0) {
            throw new JVMSimError();
        }
        --optop;
        ReturnAddress retAddr = (ReturnAddress) operandStack[optop];
        operandStack[optop] = null; // make available for gc
        return retAddr;
    }

	void pop() {
        if (optop <= 0) {
            throw new JVMSimError();
        }
        --optop;
        operandStack[optop] = null; // make available for gc
	}
}