ASMSupport教程4.9 生成三元運算符

<p>這節咱們介紹如何用ASMSupport生成三元運算符(... ? ... : ... )運算符。咱們預計生成以下代碼：</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>對應的ASMSupport的代碼以下：</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方法將生成三元操做
			//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>其餘的都很簡單。關鍵是方法：ternary。下面咱們就介紹下這個方法：</p>

<p><font color="#f79646"><strong>public final TernaryOperator ternary(Parameterized exp1, Parameterized exp2, Parameterized exp3):</strong></font><font color="#000000">這裏有三個參數，分別對應的是三元操做從左至右填寫的參數，好比a?b:c';那麼exp1表示a，exp2表示b，exp3表示c。這裏有三點須要：</font></p>

<ul> <li><font color="#000000">exp1它對於的java代碼必須返回的是布爾型的。</font> </li>

<li>exp2和exp3對應的java代碼都是須要有返回值的。 </li>

<li>這個方法會返回一個jw.asmsupport.operators.ternary.TernaryOperator，這個對象必須被其餘asmsupport的操做方法所調用。這個很好理解，好比咱們不會單獨寫一行帶你 a?b:c,一般咱們是要將這個三元表達式複製個變量或者做爲參數傳個別的方法或者其餘的操做總之，不會獨立存在的。 </li> </ul>

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