Using a hashmap with int as key and need to change it to use long - hashmap

Question

I was given some sample code by my instructor for HashEntry class and HashMap class. I had to implement the get and put method in the HashMap for the standard probing and then linear and quadratic. I have all this working fine, I am able to get and put with any of the probing methods. The next step was to read in a .csv file and parse it so the first column is the key and the remaining columns are the rows. This all works great until my key value from the .csv goes above the valid int value. My question is how can I change the provided code to use a long as the key instead of an int.
public class HashEntry {
private int key;
private String value;
HashEntry(int key, String value) {
this.key = key;
this.value = value;
}
public int getKey() {
return key;
}
public String getValue() {
return value;
}
public void setValue(String val) {
this.value = val;
}
}
HashMap
public class HashMap {
private final static int TABLE_SIZE = 1900000;
HashEntry[] table;
HashMap() {
table = new HashEntry[TABLE_SIZE];
for (int i = 0; i < TABLE_SIZE; i++)
table[i] = null;
}
public String get(int key) {
int hash = (key % TABLE_SIZE);
while (table[hash] != null && table[hash].getKey() != key)
hash = (7 * hash + 1) % TABLE_SIZE;
if (table[hash] == null)
return "There is no value at this key";
else
return table[hash].getValue();
}
public void put(int key, String value) {
int hash = (key % TABLE_SIZE);
while (table[hash] != null && table[hash].getKey() != key)
hash = (7 * hash + 1) % TABLE_SIZE;
table[hash] = new HashEntry(key, value);
}
public void linearprobeput(int key, String value){
int i = 0;
int hash = (key % TABLE_SIZE);
//System.out.println("The hash is " + hash+ "\n");
while (table[hash] != null && table[hash].getKey() != key)
{
hash = (hash + i) % TABLE_SIZE;
i++;
//printing was to verify collisions were being managed correctly
//System.out.println("Their was a collision now trying with hash'"
//+ hash +" and an i value of "+ i+ "'\n");
}
table[hash] = new HashEntry(key, value);
}
public String linearprobeget(int key){
int hash = (key % TABLE_SIZE);
int i = 0;
while (table[hash] != null && table[hash].getKey() != key)
{
hash = (hash + i) % TABLE_SIZE;
i++;
}
if (table[hash] == null)
return "There is no value at this key";
else
return table[hash].getValue();
}
public void quadraticprobeput(int key, String value){
int i = 0;
int hash = (key % TABLE_SIZE);
//System.out.println("The hash is " + hash+ "\n");
while (table[hash] != null && table[hash].getKey() != key)
{
hash = (hash + (i*i)) % TABLE_SIZE;
i++;
//printing was to verify collisions were being managed correctly
//System.out.println("Their was a collision now trying with hash'"
//+ hash +" and an i value of "+ i+ "'\n");
}
table[hash] = new HashEntry(key, value);
}
public String quadraticprobeget(int key){
int hash = (key % TABLE_SIZE);
int i = 0;
while (table[hash] != null && table[hash].getKey() != key)
{
hash = (hash + (i*i)) % TABLE_SIZE;
i++;
}
if (table[hash] == null)
return "There is no value at this key";
else
return table[hash].getValue();
}
}
Main
HashMap upchm = new HashMap();
BufferedReader in = new BufferedReader
(new FileReader("UPCtest.csv"));
//Integer a = null;
String str=null;
ArrayList<String> lines = new ArrayList<String>();
//lines.split(",")[1]+
while((str = in.readLine()) != null){
//lines.add(str);
String[] upc= str.split(",");
Integer val = Integer.valueOf(upc[0]);
upchm.quadraticprobeput(val, upc[1]+upc[2]);
System.out.println("UPC = " + val + " Description "+upc[1]+upc[2]);
}
//change arraylist to array
//String[] upc = lines.toArray(new String[lines.size()]);
in.close();
System.out.println("\n");
System.out.println("The description for the product with upc 123 is " + upchm.quadraticprobeget(123));
System.out.println("The description for the product with upc 10344 is " + upchm.quadraticprobeget(10344));
Sample of some of the lines from the .csv
79,,INDIANA LOTTO 93,,treo 700w 123,,Wrsi Riversound cafe cd
161,,Dillons/Kroger Employee Coupon ($1.25 credit)
2158242769,288/1.12Z,GREEN SUGAR COOKIES4276 2158561631,,HOT COCOA
W/BKMK 2158769549,njhjhn,gjfhjbgkj 2160500567,2.25 oz (64)g,Dollar
Bar Rich Raspberry 2172307284,,Mixed seasonal flower bouquet
2177000074,,4 way 13 AMP Extension Lead (Wilkinson UK) 2184000098,21
oz,Christopher's Assorted Fruit Jellies 2187682888,,fairway
15400021142,9 Z,WF BOWL CLEANER (JAR 15400021159,8 Z,WF ANTIBAC LIQ
SOAP 15400021166,3 RL,WF DECORATOR VALUE 15400021173,64 Z,WF CLEAR
AMMONIA 15400021210,128 Z,WF FAB SOFT 15400021319,28 Z,WF DEGREAS
ULT DISH 15400021326,28 Z,WF LEMON ULTRA DISH 15400021340,28 Z,WF
ANTIBACT DISH LIQ 15400021364,65 Z,WF AUTO DISH DETERGE

Answer 1

You have to use long key instead of int key and cast a type when you calculate a bucket in the table:
HashEntry class
public class HashEntry {
private long key;
private String value;
}
HashMap class
public class HashMap {
private static final int TABLE_SIZE = 1900000;
private final HashEntry[] table;
public HashMap() {
// all elements are null by default
table = new HashEntry[TABLE_SIZE];
}
public String get(long key) {
int bucket = getBucket(key);
while (table[bucket] != null && table[bucket].getKey() != key) {
bucket = (7 * bucket + 1) % TABLE_SIZE;
}
return getValueByBucket(bucket, key);
}
public void put(long key, String value) {
int bucket = getBucket(key);
while (table[bucket] != null && table[bucket].getKey() != key) {
bucket = (7 * bucket + 1) % TABLE_SIZE;
}
table[bucket] = new HashEntry(key, value);
}
public void linearprobeput(long key, String value) {
int i = 0;
int bucket = getBucket(key);
//System.out.println("The hash is " + hash+ "\n");
while (table[bucket] != null && table[bucket].getKey() != key) {
bucket = (bucket + i) % TABLE_SIZE;
i++;
//printing was to verify collisions were being managed correctly
//System.out.println("Their was a collision now trying with hash'"
//+ hash +" and an i value of "+ i+ "'\n");
}
table[bucket] = new HashEntry(key, value);
}
public String linearprobeget(long key) {
int i = 0;
int bucket = getBucket(key);
while (table[bucket] != null && table[bucket].getKey() != key) {
bucket = (bucket + i) % TABLE_SIZE;
i++;
}
return getValueByBucket(bucket, key);
}
public void quadraticprobeput(long key, String value) {
int i = 0;
int bucket = getBucket(key);
//System.out.println("The hash is " + hash+ "\n");
while (table[bucket] != null && table[bucket].getKey() != key) {
bucket = (bucket + (i * i)) % TABLE_SIZE;
i++;
//printing was to verify collisions were being managed correctly
//System.out.println("Their was a collision now trying with hash'"
//+ hash +" and an i value of "+ i+ "'\n");
}
table[bucket] = new HashEntry(key, value);
}
public String quadraticprobeget(long key) {
int i = 0;
int bucket = getBucket(key);
while (table[bucket] != null && table[bucket].getKey() != key) {
bucket = (bucket + (i * i)) % TABLE_SIZE;
i++;
}
return getValueByBucket(bucket, key);
}
private static int getBucket(long key) {
// this is safe, because key % TABLE_SIZE < TABLE_SIZE which is int
return (int)(key % TABLE_SIZE);
}
private String getValueByBucket(int bucket, long key) {
return table[bucket] == null ? "There is no value at key '" + key + '\'' : table[bucket].getValue();
}
}
I think, and java.lang.HashMap uses it as well, that it is better to move HashEntry into HashMap class:
public class HashMap {
private static final int TABLE_SIZE = 1900000;
private final Entry[] table;
public HashMap() {
// all elements are null by default
table = new Entry[TABLE_SIZE];
}
//...
private static final class Entry {
private long key;
private String value;
}
}
Second, it is better to throw an exception with There is no value at key or return null. What if you have: map.put(666, "There is no value at key") - when you get this key, how do you know it this key exists or not?!