HashMapExampleTest.java

package com.examplehub.basics;

import org.junit.jupiter.api.Test;

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

import static org.junit.jupiter.api.Assertions.*;

class HashMapExampleTest {
    @Test
    void testPut() {
        HashMap<String, String> hashMap = new HashMap<>();
        hashMap.put("username", "admin");
        hashMap.put("password", "abc123");
        assertEquals("{password=abc123, username=admin}", hashMap.toString());

        assertNull(hashMap.put("bio", "Github"));
        assertEquals("Github", hashMap.put("bio", "I love coding"));
    }

    @Test
    void testAddNull() {
        HashMap<String, String> hashMap = new HashMap<>();
        hashMap.put(null, "v1");
        hashMap.put(null, "v2");
        hashMap.put(null, "v3");
        assertNotNull(hashMap.get(null));
        assertEquals("v3", hashMap.get(null));
    }

    @Test
    void testGet() {
        HashMap<String, String> hashMap = new HashMap<>();
        hashMap.put("username", "admin");
        hashMap.put("password", "abc123");
        assertEquals("admin", hashMap.get("username"));
        assertEquals("abc123", hashMap.get("password"));
        assertNull(hashMap.get("bio"));

        assertEquals("jack", hashMap.getOrDefault("user", "jack"));
    }

    @Test
    void testRemove() {
        HashMap<String, String> hashMap = new HashMap<>();
        hashMap.put("username", "admin");
        hashMap.put("password", "abc123");
        assertEquals("admin", hashMap.remove("username"));
        assertEquals("abc123", hashMap.remove("password"));
        assertNull(hashMap.remove("username"));
        assertNull(hashMap.remove("password"));
    }

    @Test
    void testSize() {
        HashMap<String, String> hashMap = new HashMap<>();
        hashMap.put("username", "admin");
        hashMap.put("password", "abc123");
        assertEquals(2, hashMap.size());

        hashMap.put("bio", "I love java");
        assertEquals(3, hashMap.size());
    }

    @Test
    void testKeySet() {
        HashMap<String, String> hashMap = new HashMap<>();
        hashMap.put("username", "admin");
        hashMap.put("password", "abc123");
        assertEquals("[password, username]", hashMap.keySet().toString());
    }

    @Test
    void testValues() {
        HashMap<String, String> hashMap = new HashMap<>();
        hashMap.put("username", "admin");
        hashMap.put("password", "abc123");
        assertEquals("[abc123, admin]", hashMap.values().toString());
    }

    @Test
    void testEmpty() {
        HashMap<String, String> hashMap = new HashMap<>();
        hashMap.put("username", "admin");
        assertFalse(hashMap.isEmpty());
        assertEquals("admin", hashMap.remove("username"));
        assertTrue(hashMap.isEmpty());
    }

    @Test
    void testEntry() {
        HashMap<String, String> hashMap = new HashMap<>();
        hashMap.put("username", "admin");
        hashMap.put("password", "abc123");
        //password->abc123
        //username->admin
        for (Map.Entry<String, String> entry : hashMap.entrySet()) {
            System.out.println(entry.getKey() + "->" + entry.getValue());
        }
    }
}