Java基础-集合

package test;

import java.util.Arrays;

public class Arr
{
    public static void main(String[] args)
    {
        int[] arr = new int[2];
        arr[0] = 1;
        arr[1] = 2;
        // arr[2] = 3; // 编译出错

        System.out.println(Arrays.toString(arr)); // 输出：[1, 2]
    }
}

List a = new ArrayList();
a.add(11);
a.add("aaa"); // 添加元素
a.get(1);     // 获取第二个元素值
a.remove(1);  // 删除第 2 个元素

LinkedList l =new LinkedList();
l.add(1);
l.add(2);
l.getFirst(); // 获取第一个元素
l.getLast();  // 获取最后一个元素
l.remove(1); // 删除第 2 个元素

Vector v = new Vector();
v.add("aa");
v.add("bb");
v.get(1);
v.remove(1);

Stack s = new Stack();
s.push(1);
s.push(2);
s.pop(); // 抛出并删除首个元素
s.peek(); // 返回首个元素值，不删除值

ArrayQueue q = new ArrayQueue(12);
q.add(1);
q.add(2);
q.get(1);
q.size();、
q.remove(0);

ArrayDeque d = new ArrayDeque();
d.addFirst(11);
d.addLast(22);
d.pollFirst();
d.pollLast(); // 返回并删除队尾元素
d.peekLast(); // 返回但不删除队尾元素
d.peekFirst();
d.push(44);
d.pop();

PriorityQueue q = new PriorityQueue();
q.offer(1);
q.offer(2);
q.offer(3); // 插入元素
q.peek();   // 查看顶端元素
q.poll();   // 返回并删除顶端元素

// hash() 函数返回一个整数
static final int hash(Object key) {
    int h;
    return (key == null) ? 0 : (h = key.hashCode()) ^ (h >>> 16);
}

public class HashMap<K,V> extends AbstractMap<K,V>
    implements Map<K,V>, Cloneable, Serializable {
    
    // 构造函数
    public HashMap(int initialCapacity, float loadFactor) {
        if (initialCapacity < 0)
            throw new IllegalArgumentException("Illegal initial capacity: " +
                                               initialCapacity);
        if (initialCapacity > MAXIMUM_CAPACITY)
            initialCapacity = MAXIMUM_CAPACITY;
        if (loadFactor <= 0 || Float.isNaN(loadFactor))
            throw new IllegalArgumentException("Illegal load factor: " +
                                               loadFactor);
        this.loadFactor = loadFactor;
        
        // 扩容的阀值
        this.threshold = tableSizeFor(initialCapacity);
    }
    
    /**
     * 容器大小，返回 2 的幂
     * Returns a power of two size for the given target capacity.
     */
    static final int tableSizeFor(int cap) {
        int n = cap - 1;
        n |= n >>> 1;
        n |= n >>> 2;
        n |= n >>> 4;
        n |= n >>> 8;
        n |= n >>> 16;
        return (n < 0) ? 1 : (n >= MAXIMUM_CAPACITY) ? MAXIMUM_CAPACITY : n + 1;
    }
    
    // 插入元素
    public V put(K key, V value) {
        return putVal(hash(key), key, value, false, true);
    }
    
    /**
     * // 实际插入元素的方法
     * Implements Map.put and related methods.
     *
     * @param hash hash for key
     * @param key the key
     * @param value the value to put
     * @param onlyIfAbsent if true, don't change existing value
     * @param evict if false, the table is in creation mode.
     * @return previous value, or null if none
     */
    final V putVal(int hash, K key, V value, boolean onlyIfAbsent,
                   boolean evict) {
        Node<K,V>[] tab; Node<K,V> p; int n, i;
        if ((tab = table) == null || (n = tab.length) == 0)
            // resize 函数会设置扩容阀值
            n = (tab = resize()).length;
        if ((p = tab[i = (n - 1) & hash]) == null)
            tab[i] = newNode(hash, key, value, null);
        else {
            Node<K,V> e; K k;
            if (p.hash == hash &&
                ((k = p.key) == key || (key != null && key.equals(k))))
                e = p;
            else if (p instanceof TreeNode)
                e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value);
            else {
                for (int binCount = 0; ; ++binCount) {
                    if ((e = p.next) == null) {
                        p.next = newNode(hash, key, value, null);
                        if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st
                            treeifyBin(tab, hash);
                        break;
                    }
                    if (e.hash == hash &&
                        ((k = e.key) == key || (key != null && key.equals(k))))
                        break;
                    p = e;
                }
            }
            if (e != null) { // existing mapping for key
                V oldValue = e.value;
                if (!onlyIfAbsent || oldValue == null)
                    e.value = value;
                afterNodeAccess(e);
                return oldValue;
            }
        }
        ++modCount;
        if (++size > threshold)
            resize();
        afterNodeInsertion(evict);
        return null;
    }
     
    // 取 hash 
    static final int hash(Object key) {
        int h;
        return (key == null) ? 0 : (h = key.hashCode()) ^ (h >>> 16);
    }   
}

LinkedHashMap<String, Integer> l = new LinkedHashMap<>();
l.put("a", 11);
l.put("b", 22);
l.put("c", 33);
l.put("d", 44);
Iterator ita = l.entrySet().iterator();
while (ita.hasNext()) {
    Map.Entry entry = (Map.Entry) ita.next();
    System.out.println(entry.getKey() + "=" + entry.getValue());
}

// 输出：
a=11
b=22
c=33
d=44

HashSet s = new HashSet();
s.add("aa");
System.out.println(s.add("aa")); // false
System.out.println(s.add("bb")); // true