ClassCastException: java.lang.string cannot be cast to Object

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randoms.21

ClassCastException: java.lang.string cannot be cast to Object

in Programming Questions • 2 years ago

Hi,
The following code:

void addRank(String title){

    ranks.add(title);

   TitleItem item = (TitleItem) ranks.get(title);
}

Gives me this error: The method get(int) in the type ArrayList is not applicable for the arguments (String)

So I changed it to:

void addRank(String title){
    int arraySize = ranks.size();
    ranks.add(title);

   TitleItem item = (TitleItem) ranks.get(arraySize);//gets most recent entry to ArrayList

}

which gives me this error: ClassCastException java.lang.String cannot be cast to SketchName$TitleItem

Can anyone explain these errors and possible alternatives to me? From looking up the last error online it seems I can't cast a string variable to a class variable... but then how does it work in the simple treemap example in Ben Frys book "Visualizing Data"?

Would really appreciate any help as I'm still learning :) thanks in advance :D

Replies(5)

thomas.di..

Re: ClassCastException: java.lang.string cannot be cast to Object

2 years ago

i think your arraylist hold objects of the type TitleItem,...but you try to add an Object of the type String.

something like this should work:

ArrayList<TitleItem> ranks = new ArrayList<TitleItem>();
void setup() {
addRank(new TitleItem());
}
void addRank(TitleItem title) {
int arraySize = ranks.size();
ranks.add(title);
TitleItem item = ranks.get(arraySize);//gets most recent entry to ArrayList
}
class TitleItem{
// whatever
}

randoms.21

Re: Re: ClassCastException: java.lang.string cannot be cast to Object

2 years ago

Thanks Thomas, that would work only my main setup method is as follows:

void setup() {
size(800, 800);
smooth();

RankMap mapData = new RankMap();

String[] test = loadStrings("university.txt");
String[] retest = splitTokens(test[0], ",");

for (int i = 0; i < retest.length; i++) {
mapData.addRank(retest[i]);// this is a String which I cannot cast to type TitleItem
}

I need to add the words or titles from the text file to the ArrayList. My code is very similar to the example in Frys book so I don't understand why it doesn't work :-/

PhiLho

Re: ClassCastException: java.lang.string cannot be cast to Object

2 years ago

I don't understand your addRank function. Why do you get back an item you just put. Why not use the parameter directly? We also don't know how rank is defined nor what is a TitleItem and why you try to get one from this list.

randoms.21

Re: ClassCastException: java.lang.string cannot be cast to Object

2 years ago

Yes, I should have been more clear. I will provide my RankMap and TitleItem classes here, both larely based on the book example. My algorithm has some large holes in it because I'm still working it out so please bare with me.

class RankMap extends SimpleMapModel {
ArrayList<TitleItem> ranks;// <TitleItem> added at Thomas' suggestion (thanks)

RankMap(){

    ranks = new ArrayList<TitleItem>();

}

/*What I want addRank(title) to do is convert the ranks received as a string to a TitleItem object and fill the arrayList with these objects so the arraylist can be sorted in ascending order and then the treemap nodes can be drawn according to their position in the arrayList. Position 1 will be the smallest, the incrementSize() function added by Ben Fry will be used for subsequent positions. This is the part of my algorithm I am stuck at, at the moment :)*/

void addRank(TitleItem title){
    int arraySize = ranks.size();
    ranks.add(title);

   TitleItem item = ranks.get(arraySize);

}

void sortItems() {
   Collections.sort(ranks);// sort the ranks in the arrayList so they can be sized according to position.

}


void finishArray() {
   items = new TitleItem[ranks.size()];
   ranks.toArray(items);
}

}
class TitleItem extends SimpleMapItem {
String title;

TitleItem(String title) {
    this.title = title;
}

void draw() {
    fill(255);
    rect(x, y, w, h);

    fill(0);
    //the text is only drawn if the w and h of the text are
    //smaller than the w and h of the rect

    if(w > textWidth(title) + 6) {
      if (h > textAscent() + 6) {// textAscent() used to determine height of font
      //above baseline
        textAlign(CENTER, CENTER);
        text(title, x + w/2, y + h/2);
      }
    }
}
}

This is the rest of the code, just for good measure:

import treemap.*;

Treemap mappy;

void setup() {
size(800, 800);
smooth();

RankMap mapData = new RankMap();

String[] test = loadStrings("university.txt");
String[] retest = splitTokens(test[0], ",");//for the moment, strings are all on the same line, seperated by ","

for (int i = 0; i < retest.length; i++) {
mapData.addRank(retest[i]);
}

mapData.sortItems();
mapData.finishArray();

mappy = new Treemap(mapData, 0, 0, width, height);

noLoop();
}

void draw() {
background(255);
mappy.draw();
}

Thanks for your continued help!

PhiLho

Re: ClassCastException: java.lang.string cannot be cast to Object

2 years ago

mapData.addRank(retest[i]);// this is a String which I cannot cast to type TitleItem
becomes:
mapData.addRank(new TitleItem(retest[i])); // That's the role of the constructor!

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