Java系列-HashSet源码

1.使用HashMap来存放数据?

public class HashSet<E> extends AbstractSet<E> 
       implements Set<E>, Cloneable, java.io.Serializable {
    private transient HashMap<E,Object> map;
}

2.添加数据

实际调用的是HashMap的put方法，添加的值作为key

public class HashSet<E> extends AbstractSet<E>
    implements Set<E>, Cloneable, java.io.Serializable{

    // Dummy value to associate with an Object in the backing Map
    //为static final类型，所有的HashSet共用同一个
    private static final Object PRESENT = new Object();
    
    public boolean add(E e) {
        return map.put(e, PRESENT)==null;
    }
}

3.移除数据

实际调用的是HashMap的remove方法

public class HashSet<E> extends AbstractSet<E>
    implements Set<E>, Cloneable, java.io.Serializable {

    public boolean remove(Object o) {
        return map.remove(o)==PRESENT;
    }
}

4.判断是否包含某个数据

实际调用的是HashMap的containsKey方法

public class HashSet<E> extends AbstractSet<E>
    implements Set<E>, Cloneable, java.io.Serializable {

    public boolean contains(Object o) {
        return map.containsKey(o);
    }
}