“Lambda力学”演示示例_Java_下载.zip

import static org.junit.Assert.*; import org.junit.Test; /** * Demonstation how the JRE re-uses lambda implementation classes or instances * in different scenarios. */ public class LambdaInstancesTest { // If a non-capturing lambda is created multiple times at from the same code // the same instance is re-used. Runnable createLambda() { return LambdaInstancesTest::staticMethod; } @Test public void same_call_site() { Runnable r1 = createLambda(); Runnable r2 = createLambda(); assertSame(r1, r2); assertSame(r1.getClass(), r2.getClass()); } // For different code positions different lambda implementations are created // even if they have the same lambda body. @Test public void different_call_site() { Runnable r1 = LambdaInstancesTest::staticMethod; Runnable r2 = LambdaInstancesTest::staticMethod; assertNotSame(r1, r2); assertNotSame(r1.getClass(), r2.getClass()); } // Lambdas which capture state use a different instance on every creation // but share the same implementation class Runnable createLambdaWithCapture() { return System.out::println; } @Test public void same_call_site_with_capture() { Runnable r1 = createLambdaWithCapture(); Runnable r2 = createLambdaWithCapture(); assertNotSame(r1, r2); assertSame(r1.getClass(), r2.getClass()); } // Not everything that looks like a capture actually captures any state at // the point of lambda creation. Runnable createLambdaWithApparentCapture() { return () -> System.out.println(); } @Test public void same_call_site_with_apparent_capture() { Runnable r1 = createLambdaWithApparentCapture(); Runnable r2 = createLambdaWithApparentCapture(); assertSame(r1, r2); assertSame(r1.getClass(), r2.getClass()); } static void staticMethod() { } }