ASMSupport教程4.9 生成三元运算符

<p>这节咱们介绍如何用ASMSupport生成三元运算符(... ? ... : ... )运算符。咱们预计生成以下代码：</p> <div id="scid:9D7513F9-C04C-4721-824A-2B34F0212519:935e30cc-3321-4e00-93ba-9834f3a4e044" class="wlWriterEditableSmartContent" style="float: none; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; display: inline; padding-right: 0px"><pre class="brush: java; gutter: true; first-line: 1; tab-size: 4; toolbar: true; width: 665px; height: 206px;" style=" width: 665px; height: 206px;overflow: auto;">public static void main(String args[]) { int i = 10; int k = i &lt; 0 ? -i : i; // get absolute value of i System.out.print(&quot;Absolute value of &quot;); System.out.println(i + &quot; is &quot; + k);

i = -10;
k = i < 0 ? -i : i; // get absolute value of i
System.out.print("Absolute value of ");
System.out.println(i + " is " + k);

}</pre><!-- Code inserted with Steve Dunn's Windows Live Writer Code Formatter Plugin. http://dunnhq.com --></div>

<p>对应的ASMSupport的代码以下：</p>

<div id="scid:9D7513F9-C04C-4721-824A-2B34F0212519:4b830549-362b-47a7-b01b-d24eb59d78a7" class="wlWriterEditableSmartContent" style="float: none; padding-bottom: 0px; padding-top: 0px; padding-left: 0px; margin: 0px; display: inline; padding-right: 0px"><pre class="brush: java; gutter: true; first-line: 1; tab-size: 4; toolbar: true; width: 665px; height: 1139px;" style=" width: 665px; height: 1139px;overflow: auto;">package example.operators;

import org.objectweb.asm.Opcodes;

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 TernaryOperatorGenerate extends AbstractExample {

/**
 * @param args
 */
public static void main(String[] args) {
	
	ClassCreator creator = new ClassCreator(Opcodes.V1_5, Opcodes.ACC_PUBLIC , "generated.operators.TernaryOperatorGenerateExample", null, null);
	
	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) {
			//int i = 10;
			LocalVariable i = createVariable("i", AClass.INT_ACLASS, false, Value.value(10));
			
			//ternary方法将生成三元操做
			//int k = i < 0 ? -i : i;
			LocalVariable k = createVariable("k", AClass.INT_ACLASS, false, ternary(lessThan(i, Value.value(0)), neg(i), i));
			
			//System.out.print("Absolute value of ");
			invoke(systemOut, "print", Value.value("Absolute value of "));
			
			//System.out.println(i + " is " + k);
			invoke(systemOut, "println", append(i, Value.value(" is "), k));
			
			//i = -10;
			assign(i, Value.value(-10));
			
			//k = i < 0 ? -i : i;
			assign(k, ternary(lessThan(i, Value.value(0)), neg(i), i));

			//System.out.print("Absolute value of ");
			invoke(systemOut, "print", Value.value("Absolute value of "));
			
			//System.out.println(i + " is " + k);
			invoke(systemOut, "println", append(i, Value.value(" is "), k));
			
			runReturn();
		}
    });
	generate(creator);
}

} </pre><!-- Code inserted with Steve Dunn's Windows Live Writer Code Formatter Plugin. http://dunnhq.com --></div>

<p>其余的都很简单。关键是方法：ternary。下面咱们就介绍下这个方法：</p>

<p><font color="#f79646"><strong>public final TernaryOperator ternary(Parameterized exp1, Parameterized exp2, Parameterized exp3):</strong></font><font color="#000000">这里有三个参数，分别对应的是三元操做从左至右填写的参数，好比a?b:c';那么exp1表示a，exp2表示b，exp3表示c。这里有三点须要：</font></p>

<ul> <li><font color="#000000">exp1它对于的java代码必须返回的是布尔型的。</font> </li>

<li>exp2和exp3对应的java代码都是须要有返回值的。 </li>

<li>这个方法会返回一个jw.asmsupport.operators.ternary.TernaryOperator，这个对象必须被其余asmsupport的操做方法所调用。这个很好理解，好比咱们不会单独写一行带你 a?b:c,一般咱们是要将这个三元表达式复制个变量或者做为参数传个别的方法或者其余的操做总之，不会独立存在的。 </li> </ul>

<p><a href="http://www.wensiqun.com/download/118/">更多实例下载</a></p>