Java consumes too much memory

Question

my Java written application consumes way too much memory.

How does program work : User selects a date from calendar (GUI) and application loads data into JTable component. Everytime data is loaded, new TableModel is created and set. No new JTable is created, just model.

What is the problem? : every new day selection from calendar and loading to JTable consumes about 2-3 MB of memory. On start app consumes cca 50-60 MB of RAM, after few "clicks" on calendar (like 20), application consumes full Heap Size (128MB). Application crashes, of course ...

What should I do? : I am pretty sure database querys are OK. I might somehow set bigger heap size (I googled, but that would be only solution for my computer, users wont do this) OR I should somehow remove old TableModel with DB data. But shouldn't this be Garbage collector's work? I am able to force it (System.gc()) but that doesn't help ...

Thank you for any advice!

EDIT : Code for Handling events of calendar (I deleted Javadoc, it is in my mother tongue)

package timesheet.handlers;

import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;
import java.util.List;
import org.jdesktop.swingx.JXMonthView;
import org.jdesktop.swingx.event.DateSelectionEvent;
import org.jdesktop.swingx.event.DateSelectionListener;
import timesheet.database.WorkerOperations;
import timesheet.frames.WorkerFrame;
import timesheet.logictrier.*;


public class WorkerMonthViewHandler {
    private JXMonthView monthView;
    private WorkerFrame workerFrame;
    private WorkerOperations wops;
    private Date[] week = new Date[5];
    private WorkerTasksTableHandler wtth;

    public WorkerMonthViewHandler(WorkerFrame workerFrame) {
        this.workerFrame = workerFrame;
        this.monthView = workerFrame.getWorkerMonthView();
        wops = workerFrame.getWorkerOperations(); // for DB usage
    }

    public void initMonthView() {
        List<Task> tasks = wops.getWorkerTasks(workerFrame.getWorker()); // db select
        for (Task task : tasks) {
            if (!monthView.getSelection().contains(task.getPlannedStart())) { 
                monthView.addFlaggedDates(task.getPlannedStart());
                monthView.addFlaggedDates(task.gePlannedEnd()); // not really important
            }
        }
        monthView.setSelectionDate(new Date());
        monthView.getSelectionModel().addDateSelectionListener(new DateSelectionListener() {
            public void valueChanged(DateSelectionEvent dse) {
                Date d = monthView.getSelectionDate();
                for (int i=0; i<week.length; i++) {
                    if (d.equals(week[i])) {     
                        return;
                    }
                }
                Calendar cal = new GregorianCalendar();
                cal.setTime(d);
                long dayMs = 24 * 60 * 60 * 1000;
                switch (cal.get(Calendar.DAY_OF_WEEK)) {
                    case(Calendar.MONDAY) : {
                        week[0] = new Date(cal.getTimeInMillis());
                        week[1] = new Date(cal.getTimeInMillis()+dayMs);
                        week[2] = new Date(cal.getTimeInMillis()+2*dayMs);
                        week[3] = new Date(cal.getTimeInMillis()+3*dayMs);
                        week[4] = new Date(cal.getTimeInMillis()+4*dayMs);
                    } break;
                    case (Calendar.TUESDAY) : {
                        week[0] = new Date(cal.getTimeInMillis()-dayMs);
                        week[1] = new Date(cal.getTimeInMillis());
                        week[2] = new Date(cal.getTimeInMillis()+1*dayMs);
                        week[3] = new Date(cal.getTimeInMillis()+2*dayMs);
                        week[4] = new Date(cal.getTimeInMillis()+3*dayMs);
                    } break;
                    case (Calendar.WEDNESDAY) : {
                        week[0] = new Date(cal.getTimeInMillis()-2*dayMs);
                        week[1] = new Date(cal.getTimeInMillis()-dayMs);
                        week[2] = new Date(cal.getTimeInMillis());
                        week[3] = new Date(cal.getTimeInMillis()+1*dayMs);
                        week[4] = new Date(cal.getTimeInMillis()+2*dayMs);
                    } break;
                    case (Calendar.THURSDAY) : {
                        week[0] = new Date(cal.getTimeInMillis()-3*dayMs);
                        week[1] = new Date(cal.getTimeInMillis()-2*dayMs);
                        week[2] = new Date(cal.getTimeInMillis()-1*dayMs);
                        week[3] = new Date(cal.getTimeInMillis());
                        week[4] = new Date(cal.getTimeInMillis()+1*dayMs);
                    } break;
                    case (Calendar.FRIDAY) : {
                        week[0] = new Date(cal.getTimeInMillis()-4*dayMs);
                        week[1] = new Date(cal.getTimeInMillis()-3*dayMs);
                        week[2] = new Date(cal.getTimeInMillis()-2*dayMs);
                        week[3] = new Date(cal.getTimeInMillis()-dayMs);
                        week[4] = new Date(cal.getTimeInMillis());
                    } break;
                    case (Calendar.SATURDAY) : {
                        week[0] = new Date(cal.getTimeInMillis()-5*dayMs);
                        week[1] = new Date(cal.getTimeInMillis()-4*dayMs);
                        week[2] = new Date(cal.getTimeInMillis()-3*dayMs);
                        week[3] = new Date(cal.getTimeInMillis()-2*dayMs);
                        week[4] = new Date(cal.getTimeInMillis()-dayMs);
                    } break;
                    case (Calendar.SUNDAY) : {
                        week[0] = new Date(cal.getTimeInMillis()-6*dayMs);
                        week[1] = new Date(cal.getTimeInMillis()-5*dayMs);
                        week[2] = new Date(cal.getTimeInMillis()-4*dayMs);
                        week[3] = new Date(cal.getTimeInMillis()-3*dayMs);
                        week[4] = new Date(cal.getTimeInMillis()-2*dayMs);
                    } break;
                }
                wtth = new WorkerTasksTableHandler(workerFrame,week);
                wtth.createTable(); // sets model on JTable
            }
        });
    }

    public void reportTask() {
        wtth.reportTasks(); // simple DB insert
    }
}

Using NetBeans profiler : Date taken: Sun Feb 28 14:25:16 CET 2010 File: C:...\private\profiler\java_pid4708.hprof File size: 72,2 MB

Total bytes: 62 323 264
Total classes: 3 304
Total instances: 1 344 586
Classloaders: 18
GC roots: 2 860
Number of objects pending for finalization: 0

Answer 1

Have you run a profiler like YourKit against this ? I suspect it'll show some memory leak due to references being held when they should be released. Note that System.gc() is a hint to the JVM, and doesn't force a GC cycle.

Alternatively, your application may simply require more memory than the JVM is permitted to allocate. The JVM will only allocate up to a default maximum (dependent on your platform). Try increasing this via:

java -Xmx256m {classname}

etc. to see if this fixes the problem permanently. If it doesn't, then this points to a memory leak.

Answer 2

Read Veijko Krunic's great paper How to Fix Memory Leaks in Java. He suggests a diagnostic path for similar problems.