Prefer annotations to naming patterns

    最近迷读Effective Java 2nd Edition,其中的ITEM 35: PREFER ANNOTATIONS TO NAMING PATTERNS,也就是用annotations来替代过去的使用名称模式的习惯,代码摆上:

 

// Annotation type with a parameter
import java.lang.annotation.*;

/**
 * Indicates that the annotated method is a test method that must throw the
 * designated exception to succeed.
 */
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface ExceptionTest {
	Class<? extends Exception> value();
}



// Program containing annotations with a parameter
public class Sample2 {
	@ExceptionTest(ArithmeticException.class)
	public static void m1() { // Test should pass
		int i = 0;
		i = i / i;
	}

	@ExceptionTest(ArithmeticException.class)
	public static void m2() { // Should fail (wrong exception)
		int[] a = new int[0];
		int i = a[1];
	}

	@ExceptionTest(ArithmeticException.class)
	public static void m3() {
	} // Should fail (no exception)
}



// Program to process marker annotations
import java.lang.reflect.*;

public class RunTests {
	public static void main(String[] args) throws Exception {
		int tests = 0;
		int passed = 0;
		Class<?> testClass = Class.forName("Sample2");
		for (Method m : testClass.getDeclaredMethods()) {
			if (m.isAnnotationPresent(ExceptionTest.class)) {
				tests++;
				try {
					m.invoke(null);
					System.out.printf("Test %s failed: no exception%n", m);
				} catch (InvocationTargetException wrappedEx) {
					Throwable exc = wrappedEx.getCause();
					Class<? extends Exception> excType = m.getAnnotation(ExceptionTest.class).value();
					// note the value is ArithmeticException.class
					// and test if the caused exception is the instance of the excType
					if (excType.isInstance(exc)) {
						passed++;
					} else {
						System.out.printf("Test %s failed: expected %s, got %s%n", m, excType.getName(), exc);
					}
				} catch (Exception exc) {
					System.out.println("INVALID @Test: " + m);
				}
			}
		}
		System.out.printf("Passed: %d, Failed: %d%n", passed, tests - passed);
	}
}

 

ExceptionTest是带参的annotation

测试类RunTests主要是测试Sample2类中哪个方法抛出通过annotation参数指定的异常,是则passed,否则failed

结果如下:

 

Test public static void Sample2.m2() failed: expected java.lang.ArithmeticException, got java.lang.ArrayIndexOutOfBoundsException: 1
Test public static void Sample2.m3() failed: no exception

Passed: 1, Failed: 2

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