Hashmap Concurrent

Main.java

import java.util.HashMap;

public class Main {

    public static HashMap<String, String> map = new HashMap<>();

    public static class Work implements Runnable {
        private boolean add;
        private long start;
        Work(boolean add) {
            this.add = add;
        }

        @Override
        public void run() {
            start = System.currentTimeMillis();
            while (System.currentTimeMillis() - start < 10 * 1000) {
                if (add) {
                    try {
                        map.put("1", "2");
                    } catch (Exception ignored) { }
                    try {
                        Thread.sleep(100);
                    } catch (InterruptedException ignored) {
                    }
                } else {
                    try {
                        map.remove("1");
                    } catch (Exception ignored) { }
                    try {
                        Thread.sleep(30);
                    } catch (InterruptedException ignored) {
                    }
                }
            }
        }
    }

    public static void main(String[] args) {
        Thread ta = new Thread(new Work(true));
        Thread tm1 = new Thread(new Work(false));
        Thread tm2 = new Thread(new Work(false));
        ta.start();
        tm1.start();
        tm2.start();
        long start = System.currentTimeMillis();
        while (System.currentTimeMillis() - start < 10 * 1000) {
            System.out.println(map.size());
            try {
                Thread.sleep(200);
            } catch (InterruptedException ignored) {
            }
        }

        System.out.println("Hello world.");
    }
}