hello/java/samples/java-packages/source/DemoCollection.java

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package std;

import java.io.Serializable;
import java.util.Collection;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;

/**
 *
 * @author (C)Y.D.Zakovryashin, 05.12.2022
 */
public class DemoCollection {

    public class User implements Serializable {

        private String login;
        private String password;

        public User(String login, String password) {
            this.login = login;
            this.password = password;
        }

        public String getLogin() {
            return login;
        }

        public void setLogin(String login) {
            this.login = login;
        }

        public String getPassword() {
            return password;
        }

        public void setPassword(String password) {
            this.password = password;
        }

        @Override
        public String toString() {
            return "User{" + "login=" + login + ", password=" + password + '}';
        }
    }

    public class Info implements Serializable {

        String info;

        public Info(String info) {
            this.info = info;
        }

        public String getInfo() {
            return info;
        }

        public void setInfo(String info) {
            this.info = info;
        }

        @Override
        public String toString() {
            return "Info{" + "info=" + info + '}';
        }
    }

    public static void main(String[] args) {
        DemoCollection demo = new DemoCollection();
//        demo.print(demo.init(5));
        Map<User, Info> m = demo.init();
        demo.printMap(m);
    }

    private Set<Integer> init(int size) {
        int[] ai = {123, 345, 4564, 345, 123};
        HashSet<Integer> hs = new HashSet<>();
        for (int i : ai) {
            System.out.println("Add " + i + " is "
                    + hs.add(new Integer(i)));
        }
        return hs;
    }

    private Map<User, Info> init() {
        HashMap<User, Info> hm = new HashMap<>();
        hm.put(new User("first", "12344"), new Info("first message"));
        hm.put(new User("second", "283479"), new Info("secondt message"));
        return hm;
    }

    private <T> void printIterator(Collection<T> c) {
        if (c == null || c.isEmpty()) {
            System.out.println("Collection is null or empty");
            return;
        }
        Iterator<T> i = c.iterator();
        while (i.hasNext()) {
            T t = i.next();
            System.out.println(t);
        }
    }

    private <T> void print(Collection<T> c) {
        if (c == null || c.isEmpty()) {
            System.out.println("Collection is null or empty");
            return;
        }
        for (T t : c) {
            System.out.println(t);
        }
    }

    private void printMap(Map<User, Info> m) {
        // 1. Map.Entry
        for (Map.Entry<User, Info> tm : m.entrySet()) {
            System.out.println( tm.getKey() + " --> "
                    + tm.getValue());
        }
        System.out.println("------------------------------");
        // 2. keySet -> get(...)
        for (User u : m.keySet()) {
            Info i = m.get(u);
            System.out.println(u + " --> " + i);
        }
    }
}