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

开发者 https://www.devze.com 2023-03-12 02:13 出处:网络
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

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开发者_StackOverflow社区++) {
            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.


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.


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]++;
}
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