HashTable.java

import java.util.LinkedList;
import java.lang.Object;

public class HashTable {
    private final int size = 100;
    private final LinkedList<Object>[] keyValues;

    public HashTable() {
        keyValues = new LinkedList[size];
    }

    public void add(String key, Object value) {
        Integer hash = hash(key);
        LinkedList<Object> list = keyValues[hash % 100];
        if (list == null) {
            list = new LinkedList<>();
        }
        list.add(key);
        list.add(value);
        keyValues[hash % 100] = list;
    }

    public Object get(String key) {
        Integer hash = hash(key);
        LinkedList<Object> list = keyValues[hash % 100];
        int index =list.indexOf(key);
        return list.get(index+1);
    }

    private Integer hash(String key) {
        return Integer.valueOf(key.chars().sum());
    }
}

HashTableTest.java

import org.junit.Test;

import junit.framework.Assert;

public class HashTableTest {
    @Test
    public void testAddGetSimple() {
        HashTable hashTable = new HashTable();
        hashTable.add("key", 123L);
        hashTable.add("key2", "ok");
        Assert.assertEquals(123L, hashTable.get("key"));
        Assert.assertEquals("ok", hashTable.get("key2"));
    }

    public void testAddGetCollision() {
        HashTable hashTable = new HashTable();
        hashTable.add("abc", 123L);
        hashTable.add("cba", "ok");
        Assert.assertEquals(123L, hashTable.get("abc"));
        Assert.assertEquals("ok", hashTable.get("cba"));
    }
}