是否有一种方法可以在Java方法中传递回调函数?
我试图模拟的行为是一个。net委托被传递给一个函数。
我看到有人建议创建一个单独的对象，但这似乎有点过分，但我意识到有时过度是做事的唯一方法。
当前回答
创建一个接口，并在回调类中创建相同的接口属性。
interface dataFetchDelegate {
void didFetchdata(String data);
}
//callback class
public class BackendManager{
public dataFetchDelegate Delegate;
public void getData() {
//Do something, Http calls/ Any other work
Delegate.didFetchdata("this is callbackdata");
}
}
现在在你想要回调的类中实现上面的Created Interface。 同时传递你的类的“this”对象/引用回调。
public class Main implements dataFetchDelegate
{
public static void main( String[] args )
{
new Main().getDatafromBackend();
}
public void getDatafromBackend() {
BackendManager inc = new BackendManager();
//Pass this object as reference.in this Scenario this is Main Object
inc.Delegate = this;
//make call
inc.getData();
}
//This method is called after task/Code Completion
public void didFetchdata(String callbackData) {
// TODO Auto-generated method stub
System.out.println(callbackData);
}
}
其他回答
然而，我看到了我最喜欢的方式，这就是我一直在寻找的。它基本上是从这些答案中衍生出来的，但我必须将其操作得更冗余和有效。我想每个人都在期待我的创意
一针见血::
首先要做一个简单的接口
public interface myCallback {
void onSuccess();
void onError(String err);
}
现在让这个回调在你想处理结果的时候运行-更可能是在异步调用之后，你想运行一些依赖于这些结果的东西
// import the Interface class here
public class App {
public static void main(String[] args) {
// call your method
doSomething("list your Params", new myCallback(){
@Override
public void onSuccess() {
// no errors
System.out.println("Done");
}
@Override
public void onError(String err) {
// error happen
System.out.println(err);
}
});
}
private void doSomething(String param, // some params..
myCallback callback) {
// now call onSuccess whenever you want if results are ready
if(results_success)
callback.onSuccess();
else
callback.onError(someError);
}
}
doSomething是需要一些时间的函数你想给它添加一个回调来通知你结果出来了，把回调接口作为参数添加到这个方法
希望我的观点是清楚的，享受吧;)
在Java 8中，这个任务很简单，如果你想在多线程场景中使用回调，你可以像下面这样做:
public void methodA (int n, IntConsumer consumer) {
// create a thread
Thread t = new Thread(() -> {
// some time consuming operation
int result = IntStream.range(0, n).sum();
// after the result is ready do something with it.
consumer.accept(result);
});
t.start();
}
使用这个方法:
methodA(1000000, System.out::println);
我尝试使用java.lang.reflect来实现'callback'，这是一个示例:
package StackOverflowQ443708_JavaCallBackTest;
import java.lang.reflect.*;
import java.util.concurrent.*;
class MyTimer
{
ExecutorService EXE =
//Executors.newCachedThreadPool ();
Executors.newSingleThreadExecutor ();
public static void PrintLine ()
{
System.out.println ("--------------------------------------------------------------------------------");
}
public void SetTimer (final int timeout, final Object obj, final String methodName, final Object... args)
{
SetTimer (timeout, obj, false, methodName, args);
}
public void SetTimer (final int timeout, final Object obj, final boolean isStatic, final String methodName, final Object... args)
{
Class<?>[] argTypes = null;
if (args != null)
{
argTypes = new Class<?> [args.length];
for (int i=0; i<args.length; i++)
{
argTypes[i] = args[i].getClass ();
}
}
SetTimer (timeout, obj, isStatic, methodName, argTypes, args);
}
public void SetTimer (final int timeout, final Object obj, final String methodName, final Class<?>[] argTypes, final Object... args)
{
SetTimer (timeout, obj, false, methodName, argTypes, args);
}
public void SetTimer (final int timeout, final Object obj, final boolean isStatic, final String methodName, final Class<?>[] argTypes, final Object... args)
{
EXE.execute (
new Runnable()
{
public void run ()
{
Class<?> c;
Method method;
try
{
if (isStatic) c = (Class<?>)obj;
else c = obj.getClass ();
System.out.println ("Wait for " + timeout + " seconds to invoke " + c.getSimpleName () + "::[" + methodName + "]");
TimeUnit.SECONDS.sleep (timeout);
System.out.println ();
System.out.println ("invoking " + c.getSimpleName () + "::[" + methodName + "]...");
PrintLine ();
method = c.getDeclaredMethod (methodName, argTypes);
method.invoke (obj, args);
}
catch (Exception e)
{
e.printStackTrace();
}
finally
{
PrintLine ();
}
}
}
);
}
public void ShutdownTimer ()
{
EXE.shutdown ();
}
}
public class CallBackTest
{
public void onUserTimeout ()
{
System.out.println ("onUserTimeout");
}
public void onTestEnd ()
{
System.out.println ("onTestEnd");
}
public void NullParameterTest (String sParam, int iParam)
{
System.out.println ("NullParameterTest: String parameter=" + sParam + ", int parameter=" + iParam);
}
public static void main (String[] args)
{
CallBackTest test = new CallBackTest ();
MyTimer timer = new MyTimer ();
timer.SetTimer ((int)(Math.random ()*10), test, "onUserTimeout");
timer.SetTimer ((int)(Math.random ()*10), test, "onTestEnd");
timer.SetTimer ((int)(Math.random ()*10), test, "A-Method-Which-Is-Not-Exists"); // java.lang.NoSuchMethodException
timer.SetTimer ((int)(Math.random ()*10), System.out, "println", "this is an argument of System.out.println() which is called by timer");
timer.SetTimer ((int)(Math.random ()*10), System.class, true, "currentTimeMillis");
timer.SetTimer ((int)(Math.random ()*10), System.class, true, "currentTimeMillis", "Should-Not-Pass-Arguments"); // java.lang.NoSuchMethodException
timer.SetTimer ((int)(Math.random ()*10), String.class, true, "format", "%d %X", 100, 200); // java.lang.NoSuchMethodException
timer.SetTimer ((int)(Math.random ()*10), String.class, true, "format", "%d %X", new Object[]{100, 200});
timer.SetTimer ((int)(Math.random ()*10), test, "NullParameterTest", new Class<?>[]{String.class, int.class}, null, 888);
timer.ShutdownTimer ();
}
}
如果你指的是。net匿名委托，我认为Java的匿名类也可以使用。
public class Main {
public interface Visitor{
int doJob(int a, int b);
}
public static void main(String[] args) {
Visitor adder = new Visitor(){
public int doJob(int a, int b) {
return a + b;
}
};
Visitor multiplier = new Visitor(){
public int doJob(int a, int b) {
return a*b;
}
};
System.out.println(adder.doJob(10, 20));
System.out.println(multiplier.doJob(10, 20));
}
}
创建一个接口，并在回调类中创建相同的接口属性。
interface dataFetchDelegate {
void didFetchdata(String data);
}
//callback class
public class BackendManager{
public dataFetchDelegate Delegate;
public void getData() {
//Do something, Http calls/ Any other work
Delegate.didFetchdata("this is callbackdata");
}
}
现在在你想要回调的类中实现上面的Created Interface。 同时传递你的类的“this”对象/引用回调。
public class Main implements dataFetchDelegate
{
public static void main( String[] args )
{
new Main().getDatafromBackend();
}
public void getDatafromBackend() {
BackendManager inc = new BackendManager();
//Pass this object as reference.in this Scenario this is Main Object
inc.Delegate = this;
//make call
inc.getData();
}
//This method is called after task/Code Completion
public void didFetchdata(String callbackData) {
// TODO Auto-generated method stub
System.out.println(callbackData);
}
}
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