Create MyBloomFilter.java

Author: Snailclimb

source-code/start/hello-world/src/main/java/com/example/helloworld/controller/MyBloomFilter.java

@@ -0,0 +1,90 @@
+package com.example.helloworld.controller;
+
+import java.util.BitSet;
+
+public class MyBloomFilter {
+
+    public static void main(String[] args) {
+        String value1 = "https://javaguide.cn/";
+        String value2 = "https://github.com/Snailclimb";
+        MyBloomFilter filter = new MyBloomFilter();
+        System.out.println(filter.contains(value1));
+        System.out.println(filter.contains(value2));
+        filter.add(value1);
+        filter.add(value2);
+        System.out.println(filter.contains(value1));
+        System.out.println(filter.contains(value2));
+    }
+
+    /**
+     * 位数组的大小
+     */
+    private static final int DEFAULT_SIZE = 2 << 24;
+    /**
+     * 通过这个数组可以创建 6 个不同的哈希函数
+     */
+    private static final int[] SEEDS = new int[]{3, 13, 46, 71, 91, 134};
+
+    /**
+     * 位数组。数组中的元素只能是 0 或者 1
+     */
+    private BitSet bits = new BitSet(DEFAULT_SIZE);
+
+    /**
+     * 存放包含 hash 函数的类的数组
+     */
+    private SimpleHash[] func = new SimpleHash[SEEDS.length];
+
+    /**
+     * 初始化多个包含 hash 函数的类的数组，每个类中的 hash 函数都不一样
+     */
+    public MyBloomFilter() {
+        // 初始化多个不同的 Hash 函数
+        for (int i = 0; i < SEEDS.length; i++) {
+            func[i] = new SimpleHash(DEFAULT_SIZE, SEEDS[i]);
+        }
+    }
+
+    /**
+     * 添加元素到位数组
+     */
+    public void add(Object value) {
+        for (SimpleHash f : func) {
+            bits.set(f.hash(value), true);
+        }
+    }
+
+    /**
+     * 判断指定元素是否存在于位数组
+     */
+    public boolean contains(Object value) {
+        boolean ret = true;
+        for (SimpleHash f : func) {
+            ret = ret && bits.get(f.hash(value));
+        }
+        return ret;
+    }
+
+    /**
+     * 静态内部类。用于 hash 操作！
+     */
+    public static class SimpleHash {
+
+        private int cap;
+        private int seed;
+
+        public SimpleHash(int cap, int seed) {
+            this.cap = cap;
+            this.seed = seed;
+        }
+
+        /**
+         * 计算 hash 值
+         */
+        public int hash(Object value) {
+            int h;
+            return (value == null) ? 0 : Math.abs(seed * (cap - 1) & ((h = value.hashCode()) ^ (h >>> 16)));
+        }
+
+    }
+}