InvocationTargetException
package zad31;
import javax.swing.*;
import java.awt.event.*;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.*;
import java.lang.reflect.*;
public class Exec1 extends JFrame implements ActionListener {
int k = 0;
int n = 15;
JTextArea ta = new JTextArea(40,20);
List<Future> taskList= new ArrayList<Future>();
Exec1() {
add(new JScrollPane(ta));
JPanel p = new JPanel();
JButton b = new JButton("Start1");
b.setActionCommand("Start1");
b.addActionListener(this);
p.add(b);
b = new JButton("Start2");
b.setActionCommand("Start2");
b.addActionListener(this);
p.add(b);
b = new JButton("Start3");
b.setActionCommand("Start3");
b.addActionListener(this);
p.add(b);
b = new JButton("Stop1");
b.setActionCommand("Stop1");
b.addActionListener(this);
p.add(b);
b = new JButton("Stop2");
b.setActionCommand("Stop2");
b.addActionListener(this);
p.add(b);
b = new JButton("Stop3");
b.setActionCommand("Stop3");
b.addActionListener(this);
p.add(b);
b = new JButton("Result1");
b.setActionCommand("Result1");
b.addActionListener(this);
p.add(b);
b = new JButton("Result2");
b.setActionCommand("Result2");
b.addActionListener(this);
p.add(b);
b = new JButton("Result3");
b.setActionCommand("Result3");
b.addActionListener(this);
p.add(b);
b = new JButton("Shutdown");
b.addActionListener(this);
p.add(b);
b = new JButton("ShutdownNow");
b.addActionListener(this);
p.add(b);
add(p, "South");
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
pack();
setVisible(true);
}
public void actionPerformed(ActionEvent e) {
String cmd = e.getActionCommand();
try {
Method m = this.getClass().getDeclaredMethod("task"+cmd);
m.invoke(this);
} catch(Exception exc) { exc.printStackTrace(); }
}
class SumTask implements Callable<Integer> {
private int taskNum,
limit;
public SumTask(int taskNum, int limit) {
this.taskNum = taskNum;
this.limit = limit;
}
public Integer call() throws Exception {
int sum = 0;
for (int i = 1; i <= limit; i++) {
if (Thread.currentThread().isInterrupted()) return null;
sum+=i;
ta.append("Task " + taskNum + " part result = " + sum + '\n');
Thread.sleep(1000);
}
return sum;
}
};
Future<Integer> task;
//ExecutorService exec = Executors.newSingleThreadExecutor();
ExecutorService exec = Executors.newFixedThreadPool(3);
public void taskStart1() {
try {
taskList.add(task);
task = exec.submit(new SumTask(++k, 15));
} catch(RejectedExecutionException exc) {
ta.append("Execution rejected\n");
return;
}
ta.append("Task " + k + " submitted\n");
}
public void taskStart2() {
try {
taskList.add(task);
task = exec.submit(new SumTask(++k, 15));
} catch(RejectedExecutionException exc) {
ta.append("Execution rejected\n");
return;
}
ta.append("Task " + k + " submitted\n");
}
public void taskStart3() {
try {
taskList.add(task);
task = exec.submit(new SumTask(++k, 15));
} catch(RejectedExecutionException exc) {
ta.append("Execution rejected\n");
return;
}
ta.append("Task " + k + " submitted\n");
}
public void taskResult1() {
task=taskList.get(0);
String msg = "";
if (task.isCancelled()) msg = "Task cancelled.";
else if (task.isDone()) {
try {
msg = "Ready. Result = " + task.get();
} catch(Exception exc) {
msg = exc.getMessage();
}
}
else msg = "Task is running or waiting for execution";
JOptionPane.showMessageDialog(null, msg);
}
public void taskResult2() {
task=taskList.get(1);
String msg = "";
if (task.isCancelled()) msg = "Task cancelled.";
else if (task.isDone()) {
try {
msg = "Ready. Result = " + task.get();
} catch(Exception exc) {
msg = exc.getMessage();
}
}
else msg = "Task is running or waiting for execution";
JOptionPane.showMessageDialog(null, msg);
}
public void taskResult3() {
task=taskList.get(2);
String msg = "";
if (task.isCancelled()) msg = "Task cancelled.";
else if (task.isDone()) {
try {
msg = "Ready. Result = " + task.get();
} catch(Exception exc) {
msg = exc.getMessage();
}
}
else msg = "Task is running or waiting for execution";
JOptionPane.showMessageDialog(null, msg);
}
public void taskStop1() {
task=taskList.get(0);
task.cancel(true);
ta.append("Task 1 stopped.");
}
public void taskStop2() {
task=taskList.get(1);
task.cancel(true);
ta.append("Task 2 stopped.");
}
public void taskStop3() {
task=taskList.get(2);
task.cancel(true);
ta.append("Task 3 stopped.");
}
public void taskShutdown() {
exec.shutdown();
ta.append("Executor shutdown\n");
}
public void taskShutdownNow() {
List<Runnable> awaiting = exec.shutdownNow();
ta.append("Executor shutdown now - awaiting tasks:\n");
for (Runnable r : awaiting) {
ta.append(r.getClass().getName()+'\n');
}
}
public static void main(String[] args) {
new Exec1();
}
}
i get InvocationTargetException and java.lang.NullPointerException when i click eg button stop1 why it doesnt find the task eg task=taskList.get(0);
