Question

请查看以下Java Card程序。它们在逻辑上似乎相同，但在实践中有不同的输出：

使用switch ... case的简单传入APDU命令分析器：

package testPack;

import javacard.framework.APDU;
import javacard.framework.Applet;
import javacard.framework.ISO7816;
import javacard.framework.ISOException;

public class TestApp extends Applet {

    private TestApp() {
    }

    public static void install(byte bArray[], short bOffset, byte bLength) throws ISOException {
        new TestApp().register();
    }

    public void process(APDU arg0) throws ISOException {
        if (selectingApplet()) {
            return;
        }

        byte[] buffer = arg0.getBuffer();
        byte ins = buffer[ISO7816.OFFSET_INS];

        switch (ins) {
        case (byte) 0x80:
            ISOException.throwIt((short) 0x6901);
            break;
        default:
            ISOException.throwIt((short) 0x6902);
            break;
        }
    }
}

使用if ... else ...的相同程序：

package testPack;

import javacard.framework.APDU;
import javacard.framework.Applet;
import javacard.framework.ISO7816;
import javacard.framework.ISOException;

public class TestApp extends Applet {

    private TestApp() {
    }

    public static void install(byte bArray[], short bOffset, byte bLength) throws ISOException {
        new TestApp().register();
    }

    public void process(APDU arg0) throws ISOException {
        if (selectingApplet()) {
            return;
        }

        byte[] buffer = arg0.getBuffer();
        byte ins = buffer[ISO7816.OFFSET_INS];

        if (ins == (byte) 0x80) {
            ISOException.throwIt((short) 0x6901);
        } else {
            ISOException.throwIt((short) 0x6902);
        }
    }
}

众所周知，在Java Card中，APDU缓冲区头字段被视为有符号字节。所以我认为在回复00 80 00 00 00 APDU命令时，我必须为上述两个程序收到69 02。

但这是结果：

第一个程序：

Download Cap begin...
Download Cap successful.
Install Applet begin...
Install Applet successful.
Select Applet begin...
Select Applet successful.
Send: 00 80 00 00 00
Recv: 69 01

第二个计划：

Download Cap begin...
Download Cap successful.
Install Applet begin...
Install Applet successful.
Select Applet begin...
Select Applet successful.
Send: 00 80 00 00 00
Recv: 69 02

为什么回答不同？

Answer 1

java没有任何问题。这段代码：

byte ins = (byte) 0x80;

switch (ins) {
    case (byte) 0x80:
        System.out.println("switch matched");
        break;
    default:
        System.out.println("switch missed");
}

if (ins == (byte) 0x80) {
    System.out.println("if matched");
} else {
    System.out.println("if missed");
}

产生

switch matched
if matched

问题出在其他地方。

值得注意的是(byte) 0x80会产生-128。

Java / Java Card中的“Switch Case”和“If ... else ..”的区别

1 个答案: