Re: A java program (MyHashTable)

On Apr 22, 7:17 pm, Sagarika <SonamSenSha...@xxxxxxxxx> wrote:
I am new in this group.So,if somehow my way of posting goes wrong
please pardon.

I made a program as MyHashTable described below.All I want to print
all the elements in the hashtable as a string.What should I do? Can
you help me?

import java.io.*;
import java.util.*;
import java.util.Comparator;

interface HashComparator{
boolean isComparable(Object key);
boolean isEqualTo(Object Key1,Object Key2);
int hashValue(Object key);
}

interface HashTable {
int size();
boolean present(int p);
boolean isEmpty(int e);
Object key(int k);
Object element(int e);
Object findElement(Object key);
void insert(Object key,Object element);
Object removeElement(Object key);
}

class InvalidKeyException extends RuntimeException {
InvalidKeyException(String message) {
super(message);
}

}

class HashTableFullException extends RuntimeException {
HashTableFullException(String message) {
super(message);
}

}

class data {
Object key,element;

data() {
key = null;
element = null;
}

data(Object k,Object e){
key = k;
element = e;
}

public Object key(){ return key;}
public Object element(){ return element; }
public void setKey(Object k) { key = k; }
public void setElement(Object e) { element = e; }
}

public class MyHashTable implements HashTable {

static data PRESENT = new data();

int m,n;

data[] bucket;
Object NON_EXISTENT_KEY;

private static HashComparator C;

public MyHashTable(HashComparator C1){
n = 0;
C = C1;
m = 200;
bucket = new data[m];
}

public MyHashTable(HashComparator C1,int i){
n = 0;
C = C1;
m = i;
bucket = new data[m];
}

void examine(Object Key){
try {
if(!C.isComparable(Key)) throw new
InvalidKeyException("The key is not valid");
}
catch(NullPointerException n) { }
}

public boolean present(int x){ return (bucket[x] ==
PRESENT); }

public boolean isEmpty(int y){ return (bucket[y] == null); }

public Object key(int k) { return bucket[k].key();}

public Object element(int e) { return bucket[e].element();}

public int size() { return n; }

int findData(Object key) throws InvalidKeyException {
examine(key);
int x = C.hashValue(key) % m;
int y = x;
do {
if(isEmpty(x)) return -1;
if(present(x)) x = (x+1) % m;
else if (C.isEqualTo(key(x),key))
return x;
else
x = (x+1) % m;
}while(x != y);
return -1;
}

public Object findElement (Object key) throws
InvalidKeyException {
int x = findData(key);
if(x < 0) return this.NON_EXISTENT_KEY;
return element(x);
}

public void insert(Object key,Object element) throws
InvalidKeyException {
examine(key);
try {
int x = C.hashValue(key) % m;
int y = x;
do {
if(isEmpty(x) || present(x)) {
bucket[x] = new data(key,element);
return;
}
x = (x+1) % m;
}while(x != y);
throw new HashTableFullException("Hash table is full.
");
}
catch(NullPointerException n) { }
n++;
}

public Object remove(Object key) throws InvalidKeyException{
int x = findData(key);
if(x<0) return this.NON_EXISTENT_KEY;
Object O = element(x);
bucket[x] = PRESENT;
n--;
return O;
}

public static void main(String[] args) {
MyHashTable T = new MyHashTable(C);
try{
T.insert(new Integer(1),new Integer(29));
T.insert(new Integer(2),new Integer(45));
T.insert(new Integer(3),new Integer(37));
T.insert(new Integer(4),new Integer(99));
T.insert(new Integer(5),new Integer(58));
T.insert(new Integer(6),new Integer(76));
T.remove(new Integer(2));
System.out.println(); System.out.println();
System.out.println("The table size is " + T.size());
System.out.println();
}
catch(InvalidKeyException e) {
System.out.println("The key is Invalid");
System.out.println(e.getMessage());
}
}

}

I have implemented toString function but all that it prints all the
elements present in the hash table to be null why is it so?
import java.io.*;
import java.util.*;
import java.util.Comparator;

interface HashComparator{
boolean isComparable(Object key);
boolean isEqualTo(Object Key1,Object Key2);
int hashValue(Object key);
}

interface HashTable {
int size();
boolean present(int p);
boolean isEmpty(int e);
Object key(int k);
Object element(int e);
Object findElement(Object key);
void insert(Object key,Object element);
Object remove(Object key);
}

class InvalidKeyException extends RuntimeException {
InvalidKeyException(String message) {
super(message);
}
}

class HashTableFullException extends RuntimeException {
HashTableFullException(String message) {
super(message);
}
}

class data {
Object key,element;

data() {
key = null;
element = null;
}

data(Object k,Object e){
key = k;
element = e;
}

public Object key(){ return key;}
public Object element(){ return element; }
public void setKey(Object k) { key = k; }
public void setElement(Object e) { element = e; }
}

public class MyHashTable implements HashTable {

static data PRESENT = new data();

int m,n;

data[] bucket;
Object NON_EXISTENT_KEY;

private static HashComparator C;

public MyHashTable(HashComparator C1){
n = 0;
C = C1;
m = 200;
bucket = new data[m];
}

public MyHashTable(HashComparator C1,int i){
n = 0;
C = C1;
m = i;
bucket = new data[m];
}

void examine(Object Key){
try {
if(!C.isComparable(Key)) throw new
InvalidKeyException("The key is not valid");
}
catch(NullPointerException n) { }
}

public boolean present(int x){ return (bucket[x] ==
PRESENT); }

public boolean isEmpty(int y){ return (bucket[y] == null); }

public Object key(int k) { return bucket[k].key();}

public Object element(int e) { return bucket[e].element();}

public int size() { return n; }

int findData(Object key) throws InvalidKeyException {
examine(key);
int x = C.hashValue(key) % m;
int y = x;
do {
if(isEmpty(x)) return -1;
if(present(x)) x = (x+1) % m;
else if (C.isEqualTo(key(x),key))
return x;
else
x = (x+1) % m;
}while(x != y);
return -1;
}

public Object findElement (Object key) throws
InvalidKeyException {
int x = findData(key);
if(x < 0) return this.NON_EXISTENT_KEY;
return element(x);
}

public void insert(Object key,Object element) throws
InvalidKeyException {
examine(key);
try {
int x = C.hashValue(key) % m;
int y = x;
do {
if(isEmpty(x) || present(x)) {
bucket[x] = new data(key,element);
return;
}
x = (x+1) % m;
}while(x != y);
throw new HashTableFullException("Hash table is full.
");
}
catch(NullPointerException n) { }
n++;
}

public Object remove(Object key) throws InvalidKeyException{
int x = findData(key);
if(x < 0) return this.NON_EXISTENT_KEY;
Object O = element(x);
bucket[x] = PRESENT;
n--;
return O;
}

public String ConverttoString() {
StringBuffer s = new StringBuffer();
int i = 0;
int elements = this.size();
while(elements != 0) {
s.append(" " + this.bucket[i++]);
elements -- ;
}
return s.toString();
}

public static void main(String[] args) {
MyHashTable T = new MyHashTable(C);
try{
T.insert(new Integer(1),new Integer(29));
T.insert(new Integer(2),new Integer(45));
T.insert(new Integer(3),new Integer(37));
T.insert(new Integer(4),new Integer(99));
T.insert(new Integer(5),new Integer(58));
T.insert(new Integer(6),new Integer(76));
System.out.println(); System.out.println();
System.out.println("The table size is " + T.size());
System.out.println();
System.out.println("The table is "
+T.ConverttoString());
System.out.println();
}
catch(InvalidKeyException e) {
System.out.println("The key is Invalid");
System.out.println(e.getMessage());
}
}
}

.

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