Java Random Integer 0-99

package angel;

import java.util.HashMap;
import java.util.Map;

public class RandomCounterMap extends Thread {
    private int start;
    private int end;
    private long executionTime;
    private Map<Integer, Integer> results;

    public RandomCounterMap(int start, int end) {
        this.start = start;
        this.end = end;
        this.results = new HashMap<>();
    }

    public Map<Integer, Integer> getResults() {
        return results;
    }

    public int getLength() {
        int length = 0;
        for (int value : results.values()) {
            length += value;
        }
        return length;
    }

    public long getExecutionTime() {
        return executionTime;
    }

    private int randomInt() {
        return (int) (Math.random() * 100);
    }

    @Override
    public void run() {
        long startTime = System.currentTimeMillis();
        for (int i = start; i <= end; i++) {
            int result = randomInt();
            try {
                results.put(result, results.get(result) + 1);
            } catch (NullPointerException e) {
                results.put(result, 1);
            }
        }
        long endTime = System.currentTimeMillis();
        executionTime = endTime - startTime;
    }

    public static void main(String[] args) {
        int numbers = 100_000_000;
        int numThreads = 8;
        int numbersPerThread = numbers / numThreads;

        RandomCounterMap[] calculators = new RandomCounterMap[numThreads];
        for (int i = 0; i < numThreads; i++) {
            int start = i * numbersPerThread + 1;
            int end = (i + 1) * numbersPerThread;
            calculators[i] = new RandomCounterMap(start, end);
        }

        long startTime = System.currentTimeMillis();
        for (RandomCounterMap calculator : calculators) {
            calculator.start();
        }

        for (RandomCounterMap calculator : calculators) {
            try {
                calculator.join();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        long endTime = System.currentTimeMillis();



        int totalResults = 0;
        for (int i = 0; i < calculators.length; i++) {
            System.out.println("Thread " + i + " took " + calculators[i].getExecutionTime() + "ms");
        }
        System.out.println("Time taken: " + (endTime - startTime) + "ms");
    }
}