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irasnyd |
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//import chap09.list03.Map;
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import java.io.*;
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import java.util.*;
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public class HashTable implements Map { // open addressing
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private Entry[] entries;
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private int size, used;
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private float loadFactor;
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private final Entry NIL = new Entry(null,null); // dummy
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public HashTable(int capacity, float loadFactor) {
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entries = new Entry[capacity];
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this.loadFactor = loadFactor; }
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public HashTable(int capacity) {
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this(capacity,0.75F);}
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public HashTable() {
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this(101); }
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public Object get(Object key) {
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int h=hash(key);
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for (int i=0; i<entries.length; i++) {
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int j = nextProbe(h,i);
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Entry entry=entries[j];
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if (entry==null) break;
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if (entry==NIL) continue;
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if (entry.key.equals(key)) return entry.value; // success
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}
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return null; // failure: key not found
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}
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//added these to get the interface to behave
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public Set keySet() { System.out.println("DO NOT USE keySet()!"); return null; }
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public Set entrySet() { System.out.println("DO NOT USE entrySet()!"); return null; }
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public void putAll( Map t) { System.out.println("DO NOT USE putAll()!"); }
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public Collection values() { System.out.println("DO NOT USE values()!"); return null; }
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public boolean containsValue( Object value ) { System.out.println("DO NOT USE containsValue()!"); return false; }
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public boolean containsKey( Object key ) { System.out.println("DO NOT USE containsKey()!"); return false; }
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public boolean isEmpty() { System.out.println("DO NOT USE isEmpty()!"); return false; }
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public void clear() { System.out.println("DO NOT USE clear()!"); }
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public Object put(Object key, Object value) {
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if (used>loadFactor*entries.length) rehash();
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int h=hash(key);
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for (int i=0; i<entries.length; i++) {
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int j = nextProbe(h,i);
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Entry entry=entries[j];
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if (entry==null) {
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entries[j] = new Entry(key,value);
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++size;
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++used;
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return null; // insertion success
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}
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if (entry==NIL) continue;
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if (entry.key.equals(key)) {
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Object oldValue=entry.value;
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entries[j].value = value;
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return oldValue; // update success
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}
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}
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return null; // failure: table overflow
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}
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public Object remove(Object key) {
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int h=hash(key);
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for (int i=0; i<entries.length; i++) {
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int j = nextProbe(h,i);
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Entry entry=entries[j];
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if (entry==null) break;
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if (entry==NIL) continue;
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if (entry.key.equals(key)) {
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Object oldValue=entry.value;
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entries[j] = NIL;
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--size;
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return oldValue; // success
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}
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}
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return null; // failure: key not found
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}
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public int size() {
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return size;
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}
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private class Entry {
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Object key, value;
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Entry(Object k, Object v) { key=k; value=v; }
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}
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private int hash(Object key) {
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if (key==null) throw new IllegalArgumentException();
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return (key.hashCode() & 0x7FFFFFFF) % entries.length;
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}
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private int nextProbe(int h, int i) {
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return (h + i)%entries.length; // Linear Probing
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}
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private void rehash() {
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Entry[] oldEntries = entries;
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entries = new Entry[2*oldEntries.length+1];
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for (int k=0; k<oldEntries.length; k++) {
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Entry entry=oldEntries[k];
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if (entry==null || entry==NIL) continue;
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int h=hash(entry.key);
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for (int i=0; i<entries.length; i++) {
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int j = nextProbe(h,i);
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if (entries[j]==null) {
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entries[j] = entry;
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break;
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}
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}
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}
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used = size;
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}
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}
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