Q1]

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class BlinkingText implements Runnable {
    private JLabel label;

    public BlinkingText() {
        JFrame frame = new JFrame("Blinking Text");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(400, 200);
        
        label = new JLabel("Blinking Text");
        label.setFont(new Font("Arial", Font.BOLD, 20));
        frame.add(label, BorderLayout.CENTER);

        frame.setVisible(true);
    }

    @Override
    public void run() {
        try {
            while (true) {
                Thread.sleep(500); 
                label.setVisible(!label.isVisible());
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        BlinkingText blinkingText = new BlinkingText();
        Thread thread = new Thread(blinkingText);
        thread.start();
    }
}

Q2]

import java.util.*;

public class CitySTDCode {
    private Map<String, Integer> citySTDMap;

    public CitySTDCode() {
        citySTDMap = new HashMap<>();
    }

  
    public void addCity(String cityName, int stdCode) {
        if (!citySTDMap.containsKey(cityName)) {
            citySTDMap.put(cityName, stdCode);
            System.out.println("City '" + cityName + "' added with STD code: " + stdCode);
        } else {
            System.out.println("City '" + cityName + "' already exists in the collection.");
        }
    }


    public void removeCity(String cityName) {
        if (citySTDMap.containsKey(cityName)) {
            int stdCode = citySTDMap.remove(cityName);
            System.out.println("City '" + cityName + "' with STD code " + stdCode + " removed from the collection.");
        } else {
            System.out.println("City '" + cityName + "' not found in the collection.");
        }
    }


    public void searchCity(String cityName) {
        if (citySTDMap.containsKey(cityName)) {
            int stdCode = citySTDMap.get(cityName);
            System.out.println("STD code for city '" + cityName + "': " + stdCode);
        } else {
            System.out.println("City '" + cityName + "' not found in the collection.");
        }
    }

    public static void main(String[] args) {
        CitySTDCode citySTDCode = new CitySTDCode();
        citySTDCode.addCity("New York", 212);
        citySTDCode.addCity("Los Angeles", 213);
        citySTDCode.addCity("Chicago", 312);
        citySTDCode.addCity("San Francisco", 415);

        System.out.println("\nPerforming operations:");
        citySTDCode.addCity("Los Angeles", 310); 
        citySTDCode.removeCity("Chicago");
        citySTDCode.searchCity("New York");
        citySTDCode.searchCity("Houston"); 
    }
}