ASMSupport教程4.4 自增减操作(++,--)

4.4 自增减操作(++,—)

我们知道，++和--是各种编程语言的基本操作，其作用就不解释了，直接进入正题，我们希望生成如下代码

package generated.operators;
import java.io.PrintStream;
public class CrementOperatorGenerateExample

{

public void demonstrate()

{
System.out.println("******************************demonstrate***************************");
int a = 1;
int b = 2;
b++;
int c = b;
int d = a;
a++;
c++;
System.out.println("a = " + a);
System.out.println("b = " + b);
System.out.println("c = " + c);
System.out.println("d = " + d);

}
public void incrementAndDecrement()

{
System.out.println("******************************incrementAndDecrement***************************");
int count = 10;
count++;
count--;
System.out.println("count = " + count);

}
public static void main(String[] args)

{
CrementOperatorGenerateExample currentObj = new CrementOperatorGenerateExample();
currentObj.demonstrate();
currentObj.incrementAndDecrement();

}

}

那么通过如下ASMSupport代码就能生成：

package example.operators;


import org.objectweb.asm.Opcodes;

import jw.asmsupport.block.method.common.CommonMethodBody;
import jw.asmsupport.block.method.common.StaticMethodBody;
import jw.asmsupport.clazz.AClass;
import jw.asmsupport.clazz.AClassFactory;
import jw.asmsupport.creator.ClassCreator;
import jw.asmsupport.definition.value.Value;
import jw.asmsupport.definition.variable.LocalVariable;


import example.AbstractExample;

public class CrementOperatorGenerate extends AbstractExample {

    /**
     * @param args
     */
    public static void main(String[] args) {

        ClassCreator creator = new ClassCreator(Opcodes.V1_5, Opcodes.ACC_PUBLIC , "generated.operators.CrementOperatorGenerateExample", null, null);

        /*
         * 对应java代码
         * public void demonstrate() {
         *     System.out.println("******************************demonstrate***************************");
         *     int a = 1;
         *     int b = 2;
         *     int c;
         *     int d;
         *     c = ++b;
         *     d = a++;
         *     c++;
         *     System.out.println("a = " + a);
         *     System.out.println("b = " + b);
         *     System.out.println("c = " + c);
         *     System.out.println("d = " + d);
         * }
         */
        creator.createMethod("demonstrate", null, null, null, null, Opcodes.ACC_PUBLIC, new CommonMethodBody() {
            @Override
            public void generateBody(LocalVariable... argus) {
                invoke(systemOut, "println", Value.value("******************************demonstrate***************************"));

                //int a = 1;
                LocalVariable a = createVariable("a", AClass.INT_ACLASS, false, Value.value(1));
                //int b = 2;
                LocalVariable b = createVariable("b", AClass.INT_ACLASS, false, Value.value(2));
                //int c = ++b;
                LocalVariable c = createVariable("c", AClass.INT_ACLASS, false, beforeInc(b));
                //d = a++;
                LocalVariable d = createVariable("d", AClass.INT_ACLASS, false, afterInc(a));
                //c++;
                afterInc(c);

                //System.out.println("a = " + a);
                invoke(systemOut, "println", append(Value.value("a = "), a)); 
                invoke(systemOut, "println", append(Value.value("b = "), b)); 
                invoke(systemOut, "println", append(Value.value("c = "), c)); 
                invoke(systemOut, "println", append(Value.value("d = "), d)); 
                runReturn();
            }
        });

        /*
         * java code:
         * public void incrementAndDecrement(String[] argv) {
         *    System.out.println("******************************incrementAndDecrement***************************");
         *    int count = 10;
         *    ++count;
         *    --count;
         *    System.out.println(count);
         * }
         */
        creator.createMethod("incrementAndDecrement", null, null, null, null, Opcodes.ACC_PUBLIC, new CommonMethodBody() {
            @Override
            public void generateBody(LocalVariable... argus) {
                invoke(systemOut, "println", Value.value("******************************incrementAndDecrement***************************"));
                //int count = 10;
                LocalVariable count = createVariable("count", AClass.INT_ACLASS, false, Value.value(10));
                // ++count
                beforeInc(count); 
                // --count;
                beforeDec(count); 
                // System.out.println("count = " +  count);
                invoke(systemOut, "println", append(Value.value("count = "), count));
                runReturn();
            }
        });

        creator.createStaticMethod("main", new AClass[]{AClassFactory.getProductClass(String[].class)}, new String[]{"args"}, null, null,
                Opcodes.ACC_PUBLIC + Opcodes.ACC_STATIC, new StaticMethodBody(){

            @Override
            public void generateBody(LocalVariable... argus) {
                LocalVariable currentObj = createVariable("currentObj", getMethodOwner(), false, invokeConstructor(getMethodOwner()));
                invoke(currentObj, "demonstrate");
                invoke(currentObj, "incrementAndDecrement");
                runReturn();
            }
        });
        generate(creator);
    }
}

我们主要关注的是creator.createMethod("demonstrate", null, null, null, null, Opcodes.ACC_PUBLIC, new CommonMethodBody()这份部分内容以及creator.createMethod("incrementAndDecrement", null, null, null, null, Opcodes.ACC_PUBLIC, new CommonMethodBody()部分，创建变量部分就不解释了，如果不知道的可以参数前一章ASMSupport教程2动态生成类，我们这里主要关注一下四个方法：

• beforeInc: 这个方法相当于++a操作
• afterInc:这个方法相当于a++操作
• beforeDec:这个方法相当于--a操作
• afterDec:这个方法相当于a--操作

以上四个方法都只有一个参数，参数类型是继承Crementable类型的，在ASMSupport中jw.asmsupport.definition.variable.GlobalVariable和jw.asmsupport.definition.variable.LocalVariable。也就是说我们定义的类属性和局部变量都是可以的，但是得注意，这些变量必须是可以执行++或--操作的，这也和平常java语法是一样的。

本系列教程所有实例下载地址：http://www.wensiqun.com/download/118/