Question

我是Java新手。我正在通过Programming Hub app学习。当我读取HeapSort代码时，我发现方法fnSortHeap没有返回数组，但main方法仍然可以打印出来。从我在main方法中找到的信息必须是这样的：

int arr2 [];

arr2 = fnSortHeap（arr，i - 1）;

并且在fnSortHeap方法中必须

返回数组;

class HeapSort
{
    public static void main(String a[])
    {
        int i;
        int arr[] = {1, 3, 4, 5, 2};

        System.out.println("\nUnsorted Array\n---------------");

        for (i = 0; i < arr.length; i++)
        {
            System.out.print(" " + arr[i]);
        }

        for (i = arr.length; i > 1; i--)
        {
            fnSortHeap(arr, i - 1);
        }

        System.out.println("\n\nSorted array\n---------------");

        for (i = 0; i < arr.length; i++)
        {
            System.out.print(" " + arr[i]);
        }
    }

    public static void fnSortHeap(int array[], int arr_ubound)
    {
        int i, o;
        int lChild, rChild, mChild, root, temp;

        root = (arr_ubound - 1) / 2;

        for (o = root; o >= 0; o--)
        {
            for (i = root; i >= 0; i--)
            {
                lChild = (2 * i) + 1;
                rChild = (2 * i) + 2;

                if ((lChild <= arr_ubound) && (rChild <= arr_ubound))
                {
                    if (array[rChild] >= array[lChild])
                        mChild = rChild;
                    else
                        mChild = lChild;
                }
                else
                {
                    if (rChild > arr_ubound)
                        mChild = lChild;
                    else
                        mChild = rChild;
                }

                if (array[i] < array[mChild])
                {
                    temp = array[i];
                    array[i] = array[mChild];
                    array[mChild] = temp;
                }
            }
        }

        temp = array[0];
        array[0] = array[arr_ubound];
        array[arr_ubound] = temp;
        return;
    }
}

Answer 1

Java是按值传递的。请参考java pass by value。

我认为你的问题是java.lang.NullPointerException at java.util.Objects.requireNonNull(Objects.java:203) at com.android.build.gradle.BasePlugin.lambda$configureProject$1(BasePlugin.java:438) at sun.reflect.GeneratedMethodAccessor180.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:35) at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24) at org.gradle.internal.event.AbstractBroadcastDispatch.dispatch(AbstractBroadcastDispatch.java:42) at org.gradle.internal.event.BroadcastDispatch$SingletonDispatch.dispatch(BroadcastDispatch.java:230) at org.gradle.internal.event.BroadcastDispatch$SingletonDispatch.dispatch(BroadcastDispatch.java:149) at org.gradle.internal.event.AbstractBroadcastDispatch.dispatch(AbstractBroadcastDispatch.java:58) at org.gradle.internal.event.BroadcastDispatch$CompositeDispatch.dispatch(BroadcastDispatch.java:324) at org.gradle.internal.event.BroadcastDispatch$CompositeDispatch.dispatch(BroadcastDispatch.java:234) at org.gradle.internal.event.ListenerBroadcast.dispatch(ListenerBroadcast.java:140) at org.gradle.internal.event.ListenerBroadcast.dispatch(ListenerBroadcast.java:37) at org.gradle.internal.dispatch.ProxyDispatchAdapter$DispatchingInvocationHandler.invoke(ProxyDispatchAdapter.java:93) at com.sun.proxy.$Proxy110.graphPopulated(Unknown Source) at org.gradle.execution.taskgraph.DefaultTaskGraphExecuter.execute(DefaultTaskGraphExecuter.java:126) at org.gradle.execution.SelectedTaskExecutionAction.execute(SelectedTaskExecutionAction.java:37) at org.gradle.execution.DefaultBuildExecuter.execute(DefaultBuildExecuter.java:37) at org.gradle.execution.DefaultBuildExecuter.access$000(DefaultBuildExecuter.java:23) at org.gradle.execution.DefaultBuildExecuter$1.proceed(DefaultBuildExecuter.java:43) at org.gradle.execution.DryRunBuildExecutionAction.execute(DryRunBuildExecutionAction.java:46) at org.gradle.execution.DefaultBuildExecuter.execute(DefaultBuildExecuter.java:37) at org.gradle.execution.DefaultBuildExecuter.execute(DefaultBuildExecuter.java:30) at org.gradle.initialization.DefaultGradleLauncher$ExecuteTasks.run(DefaultGradleLauncher.java:314) at org.gradle.internal.progress.DefaultBuildOperationExecutor$RunnableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:336) at org.gradle.internal.progress.DefaultBuildOperationExecutor$RunnableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:328) at org.gradle.internal.progress.DefaultBuildOperationExecutor.execute(DefaultBuildOperationExecutor.java:199) at org.gradle.internal.progress.DefaultBuildOperationExecutor.run(DefaultBuildOperationExecutor.java:110) at org.gradle.initialization.DefaultGradleLauncher.runTasks(DefaultGradleLauncher.java:204) at org.gradle.initialization.DefaultGradleLauncher.doBuildStages(DefaultGradleLauncher.java:134) at org.gradle.initialization.DefaultGradleLauncher.executeTasks(DefaultGradleLauncher.java:109) at org.gradle.internal.invocation.GradleBuildController$1.call(GradleBuildController.java:78) at org.gradle.internal.invocation.GradleBuildController$1.call(GradleBuildController.java:75) at org.gradle.internal.work.DefaultWorkerLeaseService.withLocks(DefaultWorkerLeaseService.java:152) at org.gradle.internal.invocation.GradleBuildController.doBuild(GradleBuildController.java:100) at org.gradle.internal.invocation.GradleBuildController.run(GradleBuildController.java:75) at org.gradle.tooling.internal.provider.runner.BuildModelActionRunner.run(BuildModelActionRunner.java:53) at org.gradle.launcher.exec.ChainingBuildActionRunner.run(ChainingBuildActionRunner.java:35) at org.gradle.launcher.exec.ChainingBuildActionRunner.run(ChainingBuildActionRunner.java:35) at org.gradle.tooling.internal.provider.ValidatingBuildActionRunner.run(ValidatingBuildActionRunner.java:32) at org.gradle.launcher.exec.RunAsBuildOperationBuildActionRunner$1.run(RunAsBuildOperationBuildActionRunner.java:43) at org.gradle.internal.progress.DefaultBuildOperationExecutor$RunnableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:336) at org.gradle.internal.progress.DefaultBuildOperationExecutor$RunnableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:328) at org.gradle.internal.progress.DefaultBuildOperationExecutor.execute(DefaultBuildOperationExecutor.java:199) at org.gradle.internal.progress.DefaultBuildOperationExecutor.run(DefaultBuildOperationExecutor.java:110) at org.gradle.launcher.exec.RunAsBuildOperationBuildActionRunner.run(RunAsBuildOperationBuildActionRunner.java:40) at org.gradle.tooling.internal.provider.SubscribableBuildActionRunner.run(SubscribableBuildActionRunner.java:51) at org.gradle.launcher.exec.InProcessBuildActionExecuter.execute(InProcessBuildActionExecuter.java:47) at org.gradle.launcher.exec.InProcessBuildActionExecuter.execute(InProcessBuildActionExecuter.java:30) at org.gradle.launcher.exec.BuildTreeScopeBuildActionExecuter.execute(BuildTreeScopeBuildActionExecuter.java:39) at org.gradle.launcher.exec.BuildTreeScopeBuildActionExecuter.execute(BuildTreeScopeBuildActionExecuter.java:25) at org.gradle.tooling.internal.provider.ContinuousBuildActionExecuter.execute(ContinuousBuildActionExecuter.java:80) at org.gradle.tooling.internal.provider.ContinuousBuildActionExecuter.execute(ContinuousBuildActionExecuter.java:53) at org.gradle.tooling.internal.provider.ServicesSetupBuildActionExecuter.execute(ServicesSetupBuildActionExecuter.java:57) at org.gradle.tooling.internal.provider.ServicesSetupBuildActionExecuter.execute(ServicesSetupBuildActionExecuter.java:32) at org.gradle.tooling.internal.provider.GradleThreadBuildActionExecuter.execute(GradleThreadBuildActionExecuter.java:36) at org.gradle.tooling.internal.provider.GradleThreadBuildActionExecuter.execute(GradleThreadBuildActionExecuter.java:25) at org.gradle.tooling.internal.provider.ParallelismConfigurationBuildActionExecuter.execute(ParallelismConfigurationBuildActionExecuter.java:43) at org.gradle.tooling.internal.provider.ParallelismConfigurationBuildActionExecuter.execute(ParallelismConfigurationBuildActionExecuter.java:29) at org.gradle.tooling.internal.provider.StartParamsValidatingActionExecuter.execute(StartParamsValidatingActionExecuter.java:69) at org.gradle.tooling.internal.provider.StartParamsValidatingActionExecuter.execute(StartParamsValidatingActionExecuter.java:30) at org.gradle.tooling.internal.provider.SessionFailureReportingActionExecuter.execute(SessionFailureReportingActionExecuter.java:59) at org.gradle.tooling.internal.provider.SessionFailureReportingActionExecuter.execute(SessionFailureReportingActionExecuter.java:44) at org.gradle.tooling.internal.provider.SetupLoggingActionExecuter.execute(SetupLoggingActionExecuter.java:45) at org.gradle.tooling.internal.provider.SetupLoggingActionExecuter.execute(SetupLoggingActionExecuter.java:30) at org.gradle.launcher.daemon.server.exec.ExecuteBuild.doBuild(ExecuteBuild.java:67) at org.gradle.launcher.daemon.server.exec.BuildCommandOnly.execute(BuildCommandOnly.java:36) at org.gradle.launcher.daemon.server.api.DaemonCommandExecution.proceed(DaemonCommandExecution.java:122) at org.gradle.launcher.daemon.server.exec.WatchForDisconnection.execute(WatchForDisconnection.java:37) at org.gradle.launcher.daemon.server.api.DaemonCommandExecution.proceed(DaemonCommandExecution.java:122) at org.gradle.launcher.daemon.server.exec.ResetDeprecationLogger.execute(ResetDeprecationLogger.java:26) at org.gradle.launcher.daemon.server.api.DaemonCommandExecution.proceed(DaemonCommandExecution.java:122) at org.gradle.launcher.daemon.server.exec.RequestStopIfSingleUsedDaemon.execute(RequestStopIfSingleUsedDaemon.java:34) at org.gradle.launcher.daemon.server.api.DaemonCommandExecution.proceed(DaemonCommandExecution.java:122) 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:122) at org.gradle.launcher.daemon.server.exec.LogAndCheckHealth.execute(LogAndCheckHealth.java:55) at org.gradle.launcher.daemon.server.api.DaemonCommandExecution.proceed(DaemonCommandExecution.java:122) at org.gradle.launcher.daemon.server.exec.LogToClient.doBuild(LogToClient.java:62) at org.gradle.launcher.daemon.server.exec.BuildCommandOnly.execute(BuildCommandOnly.java:36) at org.gradle.launcher.daemon.server.api.DaemonCommandExecution.proceed(DaemonCommandExecution.java:122) at org.gradle.launcher.daemon.server.exec.EstablishBuildEnvironment.doBuild(EstablishBuildEnvironment.java:82) at org.gradle.launcher.daemon.server.exec.BuildCommandOnly.execute(BuildCommandOnly.java:36) at org.gradle.launcher.daemon.server.api.DaemonCommandExecution.proceed(DaemonCommandExecution.java:122) at org.gradle.launcher.daemon.server.exec.StartBuildOrRespondWithBusy$1.run(StartBuildOrRespondWithBusy.java:50) at org.gradle.launcher.daemon.server.DaemonStateCoordinator$1.run(DaemonStateCoordinator.java:295) at org.gradle.internal.concurrent.ExecutorPolicy$CatchAndRecordFailures.onExecute(ExecutorPolicy.java:63) at org.gradle.internal.concurrent.ManagedExecutorImpl$1.run(ManagedExecutorImpl.java:46) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at org.gradle.internal.concurrent.ThreadFactoryImpl$ManagedThreadRunnable.run(ThreadFactoryImpl.java:55) at java.lang.Thread.run(Thread.java:745)方法在方法main实际上没有返回任何内容时如何打印排序数组。

如果这是问题，那么答案就在上面的链接中。无论如何，您传递数组输入，方法fnSortHeap正在将数组排序为相同的数组（不创建任何副本），Main方法正在打印相同的数组。

Java，数组返回

1 个答案: