ArrayList 中的索引越界异常

Question

Here is the error message I get:

Exception in thread "AWT-EventQueue-0" java.lang.IndexOutOfBoundsException: Index: 2, Size: 2
    at java.util.ArrayList.RangeCheck(ArrayList.java:547)
    at java.util.ArrayList.get(ArrayList.java:322)
    at pie.chart.explorer.alpha.ShowPieChart.<init>(ShowPieChart.java:28)
    at pie.chart.explorer.alpha.PieChartMain.jButton2ActionPerformed(PieChartMain.java:101)
    at pie.chart.explorer.alpha.PieChartMain.access$100(PieChartMain.java:22)
    at pie.chart.explorer.alpha.PieChartMain$2.actionPerformed(PieChartMain.java:63)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
    at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
    at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
    at java.awt.Component.processMouseEvent(Component.java:6267)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
    at java.awt.Component.processEvent(Component.java:6032)
    at java.awt.Container.processEvent(Container.java:2041)
    at java.awt.Component.dispatchEventImpl(Component.java:4630)
    at java.awt.Container.dispatchEventImpl(Container.java:2099)
    at java.awt.Component.dispatchEvent(Component.java:4460)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4577)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4238)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4168)
    at java.awt.Container.dispatchEventImpl(Container.java:2085)
    at java.awt.Window.dispatchEventImpl(Window.java:2478)
    at java.awt.Component.dispatchEvent(Component.java:4460)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)
BUILD SUCCESSFUL (total time: 14 seconds)

And here is the code:

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package pie.chart.explorer.alpha;

import java.awt.Color;
import java.awt.FlowLayout;
import java.util.ArrayList;
import java.util.Iterator;
import javax.swing.JFrame;

/**
 *
 * @author Andrew
 */
public class ShowPieChart extends JFrame {

    PiePanel pieChart;

    public ShowPieChart(ArrayList<Float> val, ArrayList<Color> col) {
        super("Pie Chart");
        int index = 1;
        setDefaultCloseOperation(JFrame.HIDE_ON_CLOSE);
        FlowLayout flow = new FlowLayout();
        pieChart = new PiePanel(val.size());
        for(Iterator<Float> i = val.iterator(); i.hasNext(); )  {
         pieChart.addSlice(col.get(index), val.get(index));
         index++;
        }
        setLayout(flow);
        add(pieChart);
        setVisible(true);
    }
}

I have tried lots of things to fix this problem, but I can't tell why I still keep getting an IndexOutOfBoundsException. To the best of my knowledge, I am pretty sure this is correct? Can you help?

Answer 1

Index intialization should be:

int index = 0;

Because the values of the index are between 0 and lenght-1

Answer 2

The exception is showing that you are trying to access index 2, but the list is only of size 2. Initialize your index variable to 0, as list indexes (like array indexes) start with 0 and run up to size()-1 .

Answer 3

The smallest change that would let you run the code without exceptions is, as others have already pointed out, setting index at 0 . But I would also completely rewrite your for loop, in what I think is a better coding style.

int dataSize = val.size();
pieChart = new PiePanel(dataSize);
for (int i = 0; i < dataSize; i++) {
    pieChart.addSlice(col.get(i), val.get(i));
}

You don't need to use an Iterator , since you never access it inside the for loop. Better use a numeric index instead, which you can introduce inside the for definition and have it automatically incremented at each pass through the loop.

Answer 4

In addition to what the others have said, you nowhere increment your iterator:

for (Iterator<Float> i = val.iterator(); i.hasNext(); ) {
    pieChart.addSlice(col.get(index), val.get(index));
    index++;
}

You need to do the following, otherwise this loop will never terminate.

for (Iterator<Float> i = val.iterator(); i.hasNext(); i.next()) …

But it's not clear what you need this iterator for anyway.

Answer 5

index variable should start from 0. If the size of the array is n then it's index starts from 0 to n-1 .

Answer 6

index should be initialised as 0.