org.openqa.selenium.ElementNotVisibleException: Element is not currently visible and so may not be interacted with
Command duration or timeout: 30 milliseconds
Build info: version: '2.52.0', revision: '4c2593cfc3689a7fcd7be52549167e5ccc93ad28', time: '2016-02-11 11:22:43'
System info: host: 'LiuKai-PC', ip: '169.254.197.141', os.name: 'Windows 7', os.arch: 'amd64', os.version: '6.1', java.version: '1.8.0_45'
Driver info: org.openqa.selenium.firefox.FirefoxDriver
Capabilities [{applicationCacheEnabled=true, rotatable=false, handlesAlerts=true, databaseEnabled=true, version=39.0.3, platform=WINDOWS, nativeEvents=false, acceptSslCerts=true, webStorageEnabled=true, locationContextEnabled=true, browserName=firefox, takesScreenshot=true, javascriptEnabled=true, cssSelectorsEnabled=true}]
Session ID: 7adc7b57-db02-4985-8292-3dd31ce37b6a

	at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.lang.reflect.Constructor.newInstance(Constructor.java:422)
	at org.openqa.selenium.remote.ErrorHandler.createThrowable(ErrorHandler.java:206)
	at org.openqa.selenium.remote.ErrorHandler.throwIfResponseFailed(ErrorHandler.java:158)
	at org.openqa.selenium.remote.RemoteWebDriver.execute(RemoteWebDriver.java:678)
	at org.openqa.selenium.remote.RemoteWebElement.execute(RemoteWebElement.java:327)
	at org.openqa.selenium.remote.RemoteWebElement.click(RemoteWebElement.java:85)
	at ExampleJunit.test2(ExampleJunit.java:90)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:497)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:44)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:41)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
	at org.junit.runners.BlockJUnit4ClassRunner.runNotIgnored(BlockJUnit4ClassRunner.java:79)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:71)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:49)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:193)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:52)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:191)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:42)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:184)
	at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28)
	at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:31)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:236)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:157)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:119)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:42)
	at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:234)
	at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:74)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:497)
	at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)
Caused by: org.openqa.selenium.ElementNotVisibleException: Element is not currently visible and so may not be interacted with
Build info: version: '2.52.0', revision: '4c2593cfc3689a7fcd7be52549167e5ccc93ad28', time: '2016-02-11 11:22:43'
System info: host: 'LiuKai-PC', ip: '169.254.197.141', os.name: 'Windows 7', os.arch: 'amd64', os.version: '6.1', java.version: '1.8.0_45'
Driver info: driver.version: unknown
	at <anonymous class>.fxdriver.preconditions.visible(file:///C:/Users/LiuKai/AppData/Local/Temp/anonymous5640350461632149851webdriver-profile/extensions/[email protected]/components/command-processor.js:10045)
	at <anonymous class>.DelayedCommand.prototype.checkPreconditions_(file:///C:/Users/LiuKai/AppData/Local/Temp/anonymous5640350461632149851webdriver-profile/extensions/[email protected]/components/command-processor.js:12597)
	at <anonymous class>.DelayedCommand.prototype.executeInternal_/h(file:///C:/Users/LiuKai/AppData/Local/Temp/anonymous5640350461632149851webdriver-profile/extensions/[email protected]/components/command-processor.js:12614)
	at <anonymous class>.DelayedCommand.prototype.executeInternal_(file:///C:/Users/LiuKai/AppData/Local/Temp/anonymous5640350461632149851webdriver-profile/extensions/[email protected]/components/command-processor.js:12619)
	at <anonymous class>.DelayedCommand.prototype.execute/<(file:///C:/Users/LiuKai/AppData/Local/Temp/anonymous5640350461632149851webdriver-profile/extensions/[email protected]/components/command-processor.js:12561)

解答方法：

WebDriverWait wait4 = new WebDriverWait(driver,100);
        System.out.println("3");
        wait4.until(ExpectedConditions.elementToBeClickable(By.xpath("/*//*[@id=\"sf_result\"]/div/div[1]/div[2]/div[2]/div[1]/a"))).click();