hashmap源码的简单实现

青旅半醒 2022-03-31 08:56 195阅读 0赞

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2.  [简析jvm的性能调优][jvm]
3.  [hashmap源码的简单实现][hashmap]
4.  [java运行数据区域][java]
5.  [ConcurrentHashMap的实现原理与使用][ConcurrentHashMap]

--------------------

看了hashmap的源码，打算手写一个hashmap，在工作当中虽然用不到，但是可以提升思维，通过学习源码来提升自己，下面这是我写的hashmap:

1.首先定义mymap接口

mymap.hava

package hashmapdemo;
    
    /**
     * MyMap接口,里面是主类中需要实现的方法
     * @author zhangyu
     *  
     **/
    public interface MyMap<K, V> {
        public V put(K key, V value);
    
        public V get(K key);
    
        public interface Entry<K, V> {
            public K getKey();
    
            public V getValue();
        }
    }

在mymap接口里面定义要实现的方法，后面的myhashmap去实现该接口

2.MyHashMap.java实现mymap接口里面的所有方法

package hashmapdemo;
    
    /**
     *  主体的MyHashMap
     * @author zhangyu
     * 
     **/
    public class MyHashMap<K,V> implements MyMap<K,V> {
    
        // 默认大小为 16
        private static final int DEFAULT_INITIAL_CAPACITY = 1 << 4;
        // 默认的加载因子0.75
        private static final float DEFAULT_LOAD_FACTOR = 0.75f;
        // 加载因子初始化
        private float loadFactor = 0;
        // 起始值为0
        private int initCapacity = 0;
        private Entry<K, V>[] table = null;
    
        public MyHashMap() {
            this.loadFactor = DEFAULT_LOAD_FACTOR;
            this.initCapacity = DEFAULT_INITIAL_CAPACITY;
            table = new Entry[this.initCapacity];
        }
        public MyHashMap(int initCapacity, float loadFactor) {
            this.loadFactor = loadFactor;
            this.initCapacity = initCapacity;
            table = new Entry[this.initCapacity];
        }
    
        private int hash(K key) {
            int h;
            return (key == null) ? 0 : Math.abs(h = key.hashCode());
        }
    
        @Override
        public V put(K key, V value) {
            int index = hash(key) % initCapacity;
            if (table[index] != null) {
                Entry<K, V> e = table[index];
                Entry<K, V> e2 = null;
                while (e != null) {
                    if (hash(e.key) == hash(key) && e.key.equals(key)) {
                        e.value = value;
                        return value;
                    }
                    e2 = e;
                    e = e.next;
                }
                e2.next = new Entry<>(key, value, null, index);
            } else {
                Entry<K, V> e = new Entry<>(key, value, null, index);
                table[index] = e;
            }
            return value;
        }
    
        @Override
        public V get(K key) {
            int index = hash(key) % initCapacity;
            Entry<K, V> e = table[index];
            if (e == null) {
                return null;
            }
            while (e != null) {
                if ((e.key == null && key == null) || hash(e.key) == hash(key) && e.key.equals(key)) {
                    return e.value;
                }
                e = e.next;
            }
            return null;
        }
    
        public class Entry<K, V> implements MyMap.Entry<K, V> {
            private K key;
            private V value;
            private Entry<K, V> next;
            private int index;
            public Entry(K k, V v, Entry<K, V> next, int index) {
                this.key = k;
                this.value = v;
                this.next = next;
                this.index = index;
            }
            public K getKey() {
                return key;
            }
            public V getValue() {
                return value;
            }
            public Entry getNext() {
                return next;
            }
        }
    }

这个是主体实现方法，该方法比较容易，只是简单的一部分，不涉及到resize部分;

3.测试代码;test.java

package hashmapdemo;
    
    /**
     * @author zhangyu
     **/
    public class Test {
        public static void main(String[] args) {
            MyMap<String, Object> map = new MyHashMap<>();
            map.put("name", "zhangyu");
            map.put("age", 18);
            map.put("address", "jiangsu");
            map.put("sex", "male");
            map.put(null, "zhangyu");
    
            System.out.println(map.get("name"));
            System.out.println(map.get("age"));
            System.out.println(map.get("address"));
            System.out.println(map.get("sex"));
            System.out.println(map.get(null));
        }
    }

最后测试结果:

zhangyu
    18
    jiangsu
    male
    zhangyu

[github]: https://github.com/zhangyu345293721
[minor gc_full gc]: https://blog.csdn.net/zy345293721/article/details/88629820
[jvm]: https://blog.csdn.net/zy345293721/article/details/88629007
[hashmap]: https://blog.csdn.net/zy345293721/article/details/85640605
[java]: https://blog.csdn.net/zy345293721/article/details/82252181
[ConcurrentHashMap]: https://blog.csdn.net/zy345293721/article/details/82596233