CODEWITHSUNDEEP
javavectorcomparison
user641687
user641687

Reputation:

How do I make a comparison between the objects in a vector and an int? : Java

I am trying to use an if condition to compare the objects in a vector, which represent integers, with values of type int, so that I can increment those which appear in the vector according to how many times they appear in the vector. I can't for the life of me get it to compile. Here is the code.

package countjava;
import java.util.*;

public class Count {

    public static void main(String[] args) {

        Vector vect = new Vector();
        int[] amounts = new int[100];

        for (int i = 0; i <= 9999; i++) {
            VectorIntObject intObject = 
                    new VectorIntObject((int)Math.random() * 100);
            vect.add(intObject);
        }

        Collections.sort(vect);
        for (int i =0; 1 < 40; i++) {
            System.out.println(vect.get(i));
        }

        for (int i = 0; i < 10; i++) {
            for (int j = 0; j <= 99; j++) {
                Object ourObject = vect.get(i);
                if (ourObject.getVectorIntValue() == j) {
                    amounts[j]++;
                }
            }
        }

        for (int j = 0; j <= 99; j++) {
                System.out.println(amounts[j]);
        }
    }
}

class VectorIntObject {
    int value;
    public VectorIntObject(int value) {
        this.value = value;
    }

    public int getVectorIntValue() {
        return this.value;
    }
}

The comparison should happen in the nested for loops about half way down. Any help would be much appreciated. Thanks.

Upvotes: 0

Views: 2990

Answers (2)

Jon Skeet
Jon Skeet

Reputation: 1500135

EDIT: The "unreachable" statement problem is because of this

for (int i =0; 1 < 40; i++)

1 is always less than 40, so this is an infinite loop. You meant:

for (int i = 0; i < 40; i++)

The problem is that your ourObject variable is of type Object, so you can't call getVectorIntValue on it - that's not a method declared in Object.

You should be using the collection in a generic way. That way the compiler will "know" that the collection contains VectorIntObject references.

Vector<VectorIntObject> vect = new Vector<VectorIntObject>();

// Code as before...

for (int i = 0; i < 10; i++) {
    for (int j = 0; j <= 99; j++) {
        // Note type of ourObject here, with no need to cast
        VectorIntObject ourObject = vect.get(i);
        if (ourObject.getVectorIntValue() == j) {
            amounts[j]++;
        }
    }
}

Separately, I'd recommend using ArrayList instead of Vector.

If for some reason you can't use Java 1.5 or higher, so can't use generics, you have to cast in your loop instead:

for (int i = 0; i < 10; i++) {
    for (int j = 0; j <= 99; j++) {
        VectorIntObject ourObject = (VectorIntObject) vect.get(i);
        if (ourObject.getVectorIntValue() == j) {
            amounts[j]++;
        }
    }
}

This basically has the same effect at execution-time as the generic version, but the compiler isn't able to give you as much help because it doesn't know what kind of value will be in the collection.

Upvotes: 2

Buhake Sindi
Buhake Sindi

Reputation: 89169

First of all, this will not compile:

Object ourObject = vect.get(i);
if (ourObject.getVectorIntValue() == j) {
    amounts[j]++;
}

As you're returning an Object from a vector and trying to call getVectorIntValue() without typecasting it to VectorIntObject.

If you're using JDK 5 and higher, I suggest using Generics, and assign a type to Vector

Vector<VectorIntObject> vect = new Vector<VectorIntObject>();

Then this will be valid:

VectorIntObject ourObject = vect.get(i);
if (ourObject.getVectorIntValue() == j) {
    amounts[j]++;
}

Otherwise, typecasting will do

VectorIntObject ourObject = (VectorIntObject)vect.get(i);
if (ourObject.getVectorIntValue() == j) {
    amounts[j]++;
}

Upvotes: 0

Related Questions