contentproviderheap.java

java做的WEB邮局系统

package net.wastl.webmail.misc;

import net.wastl.webmail.ui.ContentProvider;

/**
 * ContentProviderHeap.java
 *
 * This class is a simple heap structure for generating a sorted order for
 * content providers.
 *
 * Created: Mon Oct  4 13:28:09 1999
 *
 * @author Sebastian Schaffert
 * @version
 */

public class ContentProviderHeap {

    int num_entries;
    ContentProvider[] keys;

    public ContentProviderHeap(int capacity) {
	keys=new ContentProvider[capacity+1];
	num_entries=0;
    }

    protected ContentProviderHeap(int capacity,int num_entries,ContentProvider[] keys) {
	this(capacity);
	this.num_entries=num_entries;
	System.arraycopy(keys,0,this.keys,0,num_entries);
    }

    /**
     * Insert a key/value pair
     * Reorganize Heap afterwards
     */
    public void insert(ContentProvider key) {
	keys[num_entries]=key;
	num_entries++;

	
	increase(num_entries);
    }

    /**
     * Return and delete the key with the lowest long value. Reorganize Heap.
     */
    public ContentProvider next() {
	ContentProvider ret=keys[0];
	keys[0]=keys[num_entries-1];
	num_entries--;
	
	decrease(1);
	
	return ret;
    }

    public boolean isEmpty() {
	return num_entries==0;
    }

    /**
     * Remove an Object from the Heap.
     * Unfortunately not (yet) of very good complexity since we are doing 
     * a simple linear search here.
     * @param key The key to remove from the heap
     */
    public void remove(ContentProvider key) {
	for(int i=0;i<num_entries;i++) {
	    if(key.equals(keys[i])) {
		num_entries--;
		int cur_pos=i+1;
		keys[i]=keys[num_entries];
		decrease(cur_pos);
		break;
	    }
	}
    }

    /**
     * Lift an element in the heap structure
     * Note that the cur_pos is actually one larger than the position in the array!
     */
    protected void increase(int cur_pos) {
	while(cur_pos > 1 && keys[cur_pos-1].getPreferredPosition()<keys[cur_pos/2-1].getPreferredPosition()) {
	    ContentProvider tmp1=keys[cur_pos/2-1];keys[cur_pos/2-1]=keys[cur_pos-1];keys[cur_pos-1]=tmp1;
	    cur_pos /= 2;
	}
    }	    

    /**
     * Lower an element in the heap structure
     * Note that the cur_pos is actually one larger than the position in the array!
     */
    protected void decrease(int cur_pos) {
	while((cur_pos*2 <= num_entries && keys[cur_pos-1].getPreferredPosition() > keys[cur_pos*2-1].getPreferredPosition()) ||
	      (cur_pos*2+1 <=num_entries && keys[cur_pos-1].getPreferredPosition() > keys[cur_pos*2].getPreferredPosition())) {
	    int lesser_son;
	    if(cur_pos*2+1 <= num_entries) {
		lesser_son=keys[cur_pos*2-1].getPreferredPosition()<keys[cur_pos*2].getPreferredPosition()?cur_pos*2:cur_pos*2+1;
	    } else {
		lesser_son=cur_pos*2;
	    }
	    ContentProvider tmp1=keys[cur_pos-1];keys[cur_pos-1]=keys[lesser_son-1];keys[lesser_son-1]=tmp1;
	    cur_pos=lesser_son;
	}
    }	    
		
   
    public ContentProviderHeap getClone() {
	return new ContentProviderHeap(keys.length, num_entries,keys);
    }
 
} // ContentProviderHeap