本文實例講述了Java權重隨機的實現方法。分享給大家供大家參考。具體分析如下：
權重隨機在項目中經常用到，所以我把它抽象到一個工具類中。
一般實現隨機權重有兩種方式：
1. 使用一個數組存放權重對應的實際目標，比如A的權重是2，B的權重是3，那么數組長度為5， 數組前兩個存放A，后三個存放B。
然后隨機一個[0-數據長度)的數字，直接取數組對應下標的值就可以了。
優點：數據結構簡單，算法高效，實現簡單
缺點：當權重值比較大同時數據又比較多的時候，會浪費內存
2. 使用區間算法，從前到后依次疊加權重，然后隨機一個[1-權重和]的數字，再用隨機的權重依次減去每個元素的權重，當第一個小于等于0的元素就是我們找元素
這里實現可以借用Arrays的binarySearch方法。
完整實例代碼點擊此處本站下載。
貼一下代碼：
WeightMeta.java：
復制代碼代碼如下:
/**
* 建議使用RandomUtil類創建RandomMeta對象
* @author wxf on 14-5-5.
*/
public class WeightMeta<T> {
private final Random ran = new Random();
private final T[] nodes;
private final int[] weights;
private final int maxW;
public WeightMeta(T[] nodes, int[] weights) {
this.nodes = nodes;
this.weights = weights;
this.maxW = weights[weights.length - 1];
}
/**
* 該方法返回權重隨機對象
* @return
*/
public T random() {
int index = Arrays.binarySearch(weights, ran.nextInt(maxW) + 1);
if (index < 0) {
index = -1 - index;
}
return nodes[index];
}
public T random(int ranInt) {
if (ranInt > maxW) {
ranInt = maxW;
} else if(ranInt < 0){
ranInt = 1;
} else {
ranInt ++;
}
int index = Arrays.binarySearch(weights, ranInt);
if (index < 0) {
index = -1 - index;
}
return nodes[index];
}
@Override
public String toString() {
StringBuilder l1 = new StringBuilder();
StringBuilder l2 = new StringBuilder("[random]\t");
StringBuilder l3 = new StringBuilder("[node]\t\t");
l1.append(this.getClass().getName()).append(":").append(this.hashCode()).append(":\n").append("[index]\t\t");
for (int i = 0; i < weights.length; i++) {
l1.append(i).append("\t");
l2.append(weights[i]).append("\t");
l3.append(nodes[i]).append("\t");
}
l1.append("\n");
l2.append("\n");
l3.append("\n");
return l1.append(l2).append(l3).toString();
}
}
* 建議使用RandomUtil類創建RandomMeta對象
* @author wxf on 14-5-5.
*/
public class WeightMeta<T> {
private final Random ran = new Random();
private final T[] nodes;
private final int[] weights;
private final int maxW;
public WeightMeta(T[] nodes, int[] weights) {
this.nodes = nodes;
this.weights = weights;
this.maxW = weights[weights.length - 1];
}
/**
* 該方法返回權重隨機對象
* @return
*/
public T random() {
int index = Arrays.binarySearch(weights, ran.nextInt(maxW) + 1);
if (index < 0) {
index = -1 - index;
}
return nodes[index];
}
public T random(int ranInt) {
if (ranInt > maxW) {
ranInt = maxW;
} else if(ranInt < 0){
ranInt = 1;
} else {
ranInt ++;
}
int index = Arrays.binarySearch(weights, ranInt);
if (index < 0) {
index = -1 - index;
}
return nodes[index];
}
@Override
public String toString() {
StringBuilder l1 = new StringBuilder();
StringBuilder l2 = new StringBuilder("[random]\t");
StringBuilder l3 = new StringBuilder("[node]\t\t");
l1.append(this.getClass().getName()).append(":").append(this.hashCode()).append(":\n").append("[index]\t\t");
for (int i = 0; i < weights.length; i++) {
l1.append(i).append("\t");
l2.append(weights[i]).append("\t");
l3.append(nodes[i]).append("\t");
}
l1.append("\n");
l2.append("\n");
l3.append("\n");
return l1.append(l2).append(l3).toString();
}
}
RandomUtil.java：
復制代碼代碼如下:
/**
* 隨機工具類
*
* 使用權重的集合Map構建隨機元數據對象
*
* 比如：
* 我們有3個url地址，他們的權重分別為1,2,3現在我們利用RandomUtil來根據權重隨機獲取url：
*
* <p><blockquote><pre>
*
* map.put(url1, 1);
* map.put(url2, 2);
* map.put(url3, 3);
* RandomMeta<String, Integer> md = RandomUtil.buildWeightMeta(map);
* String weightRandomUrl = md.random();
*
* </pre></blockquote><p>
*
* @author wxf on 14-5-5.
*/
public class RandomUtil {
public static <T> WeightMeta<T> buildWeightMeta(final Map<T, Integer> weightMap) {
final int size = weightMap.size();
Object[] nodes = new Object[size];
int[] weights = new int[size];
int index = 0;
int weightAdder = 0;
for (Map.Entry<T, Integer> each : weightMap.entrySet()) {
nodes[index] = each.getKey();
weights[index++] = (weightAdder = weightAdder + each.getValue());
}
return new WeightMeta<T>((T[]) nodes, weights);
}
}
* 隨機工具類
*
* 使用權重的集合Map構建隨機元數據對象
*
* 比如：
* 我們有3個url地址，他們的權重分別為1,2,3現在我們利用RandomUtil來根據權重隨機獲取url：
*
* <p><blockquote><pre>
*
* map.put(url1, 1);
* map.put(url2, 2);
* map.put(url3, 3);
* RandomMeta<String, Integer> md = RandomUtil.buildWeightMeta(map);
* String weightRandomUrl = md.random();
*
* </pre></blockquote><p>
*
* @author wxf on 14-5-5.
*/
public class RandomUtil {
public static <T> WeightMeta<T> buildWeightMeta(final Map<T, Integer> weightMap) {
final int size = weightMap.size();
Object[] nodes = new Object[size];
int[] weights = new int[size];
int index = 0;
int weightAdder = 0;
for (Map.Entry<T, Integer> each : weightMap.entrySet()) {
nodes[index] = each.getKey();
weights[index++] = (weightAdder = weightAdder + each.getValue());
}
return new WeightMeta<T>((T[]) nodes, weights);
}
}
希望本文所述對大家的Java程序設計有所幫助。
