Why is my Comparator Crashing?

[dragstang86]

Why is my following Comparator Crashing? The Error Messages are below the code. Thanks for any input!

import java.util.Comparator;
import java.util.Map;


public class SortByStyle implements Comparator<Furniture>{
    
    Map theMapToSort;

    public SortByStyle(Map theMapToSort) {
        this.theMapToSort = theMapToSort;
    }

    public int compare(Furniture key1, Furniture key2) {
        
        Furniture furn = new Furniture();
        Furniture furn2 = new Furniture();
        
        furn = (Furniture) theMapToSort.get(key1.getStyle());
        furn2 = (Furniture) theMapToSort.get(key2.getStyle());
        
        if(furn.getStyle().compareToIgnoreCase(furn2.getStyle()) < 0)
        {
            return -1;
        }
        
        else{
            return 1;
        }

    }
}

Exception in thread "AWT-EventQueue-0" java.lang.ClassCastException: java.lang.Integer cannot be cast to project1.client.Furniture
	at project1.client.SortByStyle.compare(SortByStyle.java:15)
	at java.util.TreeMap.compare(TreeMap.java:1188)
	at java.util.TreeMap.put(TreeMap.java:531)
	at java.util.AbstractMap.putAll(AbstractMap.java:273)
	at java.util.TreeMap.putAll(TreeMap.java:322)
	at project1.client.Project1$ButtonListener2.actionPerformed(Project1.java:467)
	at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
	at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
	at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
	at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
	at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
	at java.awt.Component.processMouseEvent(Component.java:6504)
	at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
	at java.awt.Component.processEvent(Component.java:6269)
	at java.awt.Container.processEvent(Container.java:2229)
	at java.awt.Component.dispatchEventImpl(Component.java:4860)
	at java.awt.Container.dispatchEventImpl(Container.java:2287)
	at java.awt.Component.dispatchEvent(Component.java:4686)
	at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
	at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
	at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
	at java.awt.Container.dispatchEventImpl(Container.java:2273)
	at java.awt.Window.dispatchEventImpl(Window.java:2713)
	at java.awt.Component.dispatchEvent(Component.java:4686)
	at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:707)
	at java.awt.EventQueue.access$000(EventQueue.java:101)
	at java.awt.EventQueue$3.run(EventQueue.java:666)
	at java.awt.EventQueue$3.run(EventQueue.java:664)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
	at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
	at java.awt.EventQueue$4.run(EventQueue.java:680)
	at java.awt.EventQueue$4.run(EventQueue.java:678)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
	at java.awt.EventQueue.dispatchEvent(EventQueue.java:677)
	at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:211)
	at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:128)
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:117)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:113)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:105)
	at java.awt.EventDispatchThread.run(EventDispatchThread.java:90)

[jammas615]

java.lang.Integer cannot be cast to project1.client.Furniture

Which line in your code tries to do this?

[dragstang86]

According to the line numbering above it is line 5. The first line of the class.

[sunde887]

A few things I notice: First you should be using generic type parameters when using maps (or any other collection for that matter).

Next, the compare method should not know anything of the collection it is working on. Instead it should determine which of two items are larger.

Look here for an example of how to implement this: Object Ordering (The Java™ Tutorials > Collections > Interfaces)

[dragstang86]

I'm not sure how else I can make comparisons based upon class variables. The sort needs to be done alphabetically, in this case based upon String style, which is a member of the Furniture class.

[sunde887]

Abstract out the whole idea of using a map. Simply provide a comparator which has a method which takes two Furniture objects and returns the string comparison of them. The String class already has a comparison which returns a proper value, make use of it.

public int compare(Furniture f1, Furniture f2){
  String f1Style = ...;
  String f2Style = ...;
  return f1 style compared to f2 style
}