java - 在这种情况下如何在 java 泛型中使用多个边界

Question

我正在尝试为类似的东西创建一个构造函数。

public <T extends AppCompatActivity & DialogInterface.OnDismissListener> GooglePlayUtils(T activity) {
    this.activity = activity;
}

Android studio 对此没有任何提示，但在 CompileDebugJava 上构建失败

但是，如果删除第二个边界，编译工作正常。 我是否做错了，或者是否还缺少其他一些因素？

编辑 将类型参数添加到类本身而不是构造函数后，为我解决了这个问题。但我仍然保留这个问题，以便有人可以解释为什么会这样？

编辑2 将类型参数添加到类而不是构造函数

public abstract class GooglePlayUtils<T extends AppCompatActivity & DialogInterface.OnDismissListener> {

private T activity;

public GooglePlayUtils(T activity) {
    this.activity = activity;
}

错误

java.lang.AssertionError: at com.sun.tools.javac.util.Assert.error(Assert.java:133) at com.sun.tools.javac.util.Assert.check(Assert.java:86) at com.sun.tools.javac.comp.Attr.attribBounds(Attr.java:561) at com.sun.tools.javac.comp.Attr.visitMethodDef(Attr.java:723) at com.sun.tools.javac.tree.JCTree$JCMethodDecl.accept(JCTree.java:669) at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:431) at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:418) at com.sun.tools.javac.comp.Attr.attribStat(Attr.java:480) at com.sun.tools.javac.comp.Attr.attribClassBody(Attr.java:3250) at com.sun.tools.javac.comp.Attr.attribClass(Attr.java:3173) at com.sun.tools.javac.comp.Attr.attribClass(Attr.java:3109) at com.sun.tools.javac.comp.Attr.visitClassDef(Attr.java:708) at com.sun.tools.javac.tree.JCTree$JCClassDecl.accept(JCTree.java:591) at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:431) at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:418) at com.sun.tools.javac.comp.Attr.attribStat(Attr.java:480) at com.sun.tools.javac.comp.Attr.visitNewClass(Attr.java:1790) at com.sun.tools.javac.tree.JCTree$JCNewClass.accept(JCTree.java:1372) at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:431) at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:418) at com.sun.tools.javac.comp.Attr.attribExpr(Attr.java:449) at com.sun.tools.javac.comp.Attr.visitAssign(Attr.java:1993) at com.sun.tools.javac.tree.JCTree$JCAssign.accept(JCTree.java:1466) at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:431) at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:418) at com.sun.tools.javac.comp.Attr.attribExpr(Attr.java:460) at com.sun.tools.javac.comp.Attr.visitExec(Attr.java:1294) at com.sun.tools.javac.tree.JCTree$JCExpressionStatement.accept(JCTree.java:1167) at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:431) at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:418) at com.sun.tools.javac.comp.Attr.attribStat(Attr.java:480) at com.sun.tools.javac.comp.Attr.attribStats(Attr.java:496) at com.sun.tools.javac.comp.Attr.visitBlock(Attr.java:918) at com.sun.tools.javac.tree.JCTree$JCBlock.accept(JCTree.java:781) at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:431) at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:418) at com.sun.tools.javac.comp.Attr.attribStat(Attr.java:480) at com.sun.tools.javac.comp.Attr.visitMethodDef(Attr.java:836) at com.sun.tools.javac.tree.JCTree$JCMethodDecl.accept(JCTree.java:669) at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:431) at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:418) at com.sun.tools.javac.comp.Attr.attribStat(Attr.java:480) at com.sun.tools.javac.comp.Attr.attribClassBody(Attr.java:3250) at com.sun.tools.javac.comp.Attr.attribClass(Attr.java:3173) at com.sun.tools.javac.comp.Attr.attribClass(Attr.java:3109) at com.sun.tools.javac.comp.Attr.attrib(Attr.java:3083) at com.sun.tools.javac.main.JavaCompiler.attribute(JavaCompiler.java:1184) at com.sun.tools.javac.main.JavaCompiler.compile2(JavaCompiler.java:870) at com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:829) at com.sun.tools.javac.main.Main.compile(Main.java:439) at com.sun.tools.javac.api.JavacTaskImpl.call(JavacTaskImpl.java:132) at org.gradle.api.internal.tasks.compile.JdkJavaCompiler.execute(JdkJavaCompiler.java:45) at org.gradle.api.internal.tasks.compile.JdkJavaCompiler.execute(JdkJavaCompiler.java:33) at org.gradle.api.internal.tasks.compile.NormalizingJavaCompiler.delegateAndHandleErrors(NormalizingJavaCompiler.java:101) at org.gradle.api.internal.tasks.compile.NormalizingJavaCompiler.execute(NormalizingJavaCompiler.java:50) at org.gradle.api.internal.tasks.compile.NormalizingJavaCompiler.execute(NormalizingJavaCompiler.java:36) at org.gradle.api.internal.tasks.compile.CleaningJavaCompilerSupport.execute(CleaningJavaCompilerSupport.java:34) at org.gradle.api.internal.tasks.compile.CleaningJavaCompilerSupport.execute(CleaningJavaCompilerSupport.java:25) at org.gradle.api.tasks.compile.JavaCompile.performCompilation(JavaCompile.java:157) at org.gradle.api.tasks.compile.JavaCompile.compile(JavaCompile.java:137) at org.gradle.api.tasks.compile.JavaCompile.compile(JavaCompile.java:91) at sun.reflect.GeneratedMethodAccessor1481.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:606) at org.gradle.internal.reflect.JavaMethod.invoke(JavaMethod.java:75) at org.gradle.api.internal.project.taskfactory.AnnotationProcessingTaskFactory$IncrementalTaskAction.doExecute(AnnotationProcessingTaskFactory.java:243) at org.gradle.api.internal.project.taskfactory.AnnotationProcessingTaskFactory$StandardTaskAction.execute(AnnotationProcessingTaskFactory.java:219) at org.gradle.api.internal.project.taskfactory.AnnotationProcessingTaskFactory$IncrementalTaskAction.execute(AnnotationProcessingTaskFactory.java:230) at org.gradle.api.internal.project.taskfactory.AnnotationProcessingTaskFactory$StandardTaskAction.execute(AnnotationProcessingTaskFactory.java:208) at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeAction(ExecuteActionsTaskExecuter.java:80) at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeActions(ExecuteActionsTaskExecuter.java:61) at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.execute(ExecuteActionsTaskExecuter.java:46) at org.gradle.api.internal.tasks.execution.PostExecutionAnalysisTaskExecuter.execute(PostExecutionAnalysisTaskExecuter.java:35) at org.gradle.api.internal.tasks.execution.SkipUpToDateTaskExecuter.execute(SkipUpToDateTaskExecuter.java:64) at org.gradle.api.internal.tasks.execution.ValidatingTaskExecuter.execute(ValidatingTaskExecuter.java:58) at org.gradle.api.internal.tasks.execution.SkipEmptySourceFilesTaskExecuter.execute(SkipEmptySourceFilesTaskExecuter.java:42) at org.gradle.api.internal.tasks.execution.SkipTaskWithNoActionsExecuter.execute(SkipTaskWithNoActionsExecuter.java:52) at org.gradle.api.internal.tasks.execution.SkipOnlyIfTaskExecuter.execute(SkipOnlyIfTaskExecuter.java:53) at org.gradle.api.internal.tasks.execution.ExecuteAtMostOnceTaskExecuter.execute(ExecuteAtMostOnceTaskExecuter.java:43) at org.gradle.api.internal.AbstractTask.executeWithoutThrowingTaskFailure(AbstractTask.java:310) at org.gradle.execution.taskgraph.AbstractTaskPlanExecutor$TaskExecutorWorker.executeTask(AbstractTaskPlanExecutor.java:79) at org.gradle.execution.taskgraph.AbstractTaskPlanExecutor$TaskExecutorWorker.processTask(AbstractTaskPlanExecutor.java:63) at org.gradle.execution.taskgraph.AbstractTaskPlanExecutor$TaskExecutorWorker.run(AbstractTaskPlanExecutor.java:51) at org.gradle.execution.taskgraph.DefaultTaskPlanExecutor.process(DefaultTaskPlanExecutor.java:23) at org.gradle.execution.taskgraph.DefaultTaskGraphExecuter.execute(DefaultTaskGraphExecuter.java:88) at org.gradle.execution.SelectedTaskExecutionAction.execute(SelectedTaskExecutionAction.java:37) at org.gradle.execution.DefaultBuildExecuter.execute(DefaultBuildExecuter.java:62) at org.gradle.execution.DefaultBuildExecuter.access$200(DefaultBuildExecuter.java:23) at org.gradle.execution.DefaultBuildExecuter$2.proceed(DefaultBuildExecuter.java:68) at org.gradle.execution.DryRunBuildExecutionAction.execute(DryRunBuildExecutionAction.java:32) at org.gradle.execution.DefaultBuildExecuter.execute(DefaultBuildExecuter.java:62) at org.gradle.execution.DefaultBuildExecuter.execute(DefaultBuildExecuter.java:55) at org.gradle.initialization.DefaultGradleLauncher.doBuildStages(DefaultGradleLauncher.java:149) at org.gradle.initialization.DefaultGradleLauncher.doBuild(DefaultGradleLauncher.java:106) at org.gradle.initialization.DefaultGradleLauncher.run(DefaultGradleLauncher.java:86) at org.gradle.launcher.exec.InProcessBuildActionExecuter$DefaultBuildController.run(InProcessBuildActionExecuter.java:90) at org.gradle.tooling.internal.provider.runner.BuildModelActionRunner.run(BuildModelActionRunner.java:54) at org.gradle.launcher.exec.ChainingBuildActionRunner.run(ChainingBuildActionRunner.java:35) at org.gradle.launcher.exec.InProcessBuildActionExecuter.execute(InProcessBuildActionExecuter.java:41) at org.gradle.launcher.exec.InProcessBuildActionExecuter.execute(InProcessBuildActionExecuter.java:28) at org.gradle.launcher.daemon.server.exec.ExecuteBuild.doBuild(ExecuteBuild.java:49) at org.gradle.launcher.daemon.server.exec.BuildCommandOnly.execute(BuildCommandOnly.java:36) at org.gradle.launcher.daemon.server.api.DaemonCommandExecution.proceed(DaemonCommandExecution.java:120) at org.gradle.launcher.daemon.server.exec.WatchForDisconnection.execute(WatchForDisconnection.java:37) at org.gradle.launcher.daemon.server.api.DaemonCommandExecution.proceed(DaemonCommandExecution.java:120) at org.gradle.launcher.daemon.server.exec.ResetDeprecationLogger.execute(ResetDeprecationLogger.java:26) at org.gradle.launcher.daemon.server.api.DaemonCommandExecution.proceed(DaemonCommandExecution.java:120) at org.gradle.launcher.daemon.server.exec.RequestStopIfSingleUsedDaemon.execute(RequestStopIfSingleUsedDaemon.java:34) at org.gradle.launcher.daemon.server.api.DaemonCommandExecution.proceed(DaemonCommandExecution.java:120) at org.gradle.launcher.daemon.server.exec.ForwardClientInput$2.call(ForwardClientInput.java:74) at org.gradle.launcher.daemon.server.exec.ForwardClientInput$2.call(ForwardClientInput.java:72) at org.gradle.util.Swapper.swap(Swapper.java:38) at org.gradle.launcher.daemon.server.exec.ForwardClientInput.execute(ForwardClientInput.java:72) at org.gradle.launcher.daemon.server.api.DaemonCommandExecution.proceed(DaemonCommandExecution.java:120) at org.gradle.launcher.daemon.server.health.DaemonHealthTracker.execute(DaemonHealthTracker.java:47) at org.gradle.launcher.daemon.server.api.DaemonCommandExecution.proceed(DaemonCommandExecution.java:120) at org.gradle.launcher.daemon.server.exec.LogToClient.doBuild(LogToClient.java:66) at org.gradle.launcher.daemon.server.exec.BuildCommandOnly.execute(BuildCommandOnly.java:36) at org.gradle.launcher.daemon.server.api.DaemonCommandExecution.proceed(DaemonCommandExecution.java:120) at org.gradle.launcher.daemon.server.exec.EstablishBuildEnvironment.doBuild(EstablishBuildEnvironment.java:71) at org.gradle.launcher.daemon.server.exec.BuildCommandOnly.execute(BuildCommandOnly.java:36) at org.gradle.launcher.daemon.server.api.DaemonCommandExecution.proceed(DaemonCommandExecution.java:120) at org.gradle.launcher.daemon.server.health.HintGCAfterBuild.execute(HintGCAfterBuild.java:41) at org.gradle.launcher.daemon.server.api.DaemonCommandExecution.proceed(DaemonCommandExecution.java:120) at org.gradle.launcher.daemon.server.exec.StartBuildOrRespondWithBusy$1.run(StartBuildOrRespondWithBusy.java:50) at org.gradle.launcher.daemon.server.DaemonStateCoordinator$1.run(DaemonStateCoordinator.java:246) at org.gradle.internal.concurrent.ExecutorPolicy$CatchAndRecordFailures.onExecute(ExecutorPolicy.java:54) at org.gradle.internal.concurrent.StoppableExecutorImpl$1.run(StoppableExecutorImpl.java:40) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) at java.lang.Thread.run(Thread.java:745)

Answer 1

您是否试图创建一个泛型类，或者一个其构造函数采用泛型参数的具体类？

如果您尝试创建一个通用类，则可以为扩展 AppCompatActivity & DialogInterface.OnDismissListener 的对象实例化该类。 ，您需要使该类通用(如您的编辑中所示)。在泛型类中，类类型参数不需要在构造函数定义中重复，它们由编译器隐式假定。

如果您尝试创建某个具体或泛型类型的类，其构造函数可以接受扩展 AppCompatActivity & DialogInterface.OnDismissListener 的对象，您需要一种方法将该参数显式转换为任何类型 this.activity被定义为。分配通用 activity 的唯一方法参数this.activity不进行转换是指它们在类型删除后是否是相同的类型。

虽然可以创建一个其参数为泛型的构造函数，但您无法在不进行强制转换的情况下将泛型参数分配给不同类型之一(类型删除后)。