JavaSE---集合

Posted 2021-02-09 anpeiyong

1、【ArrayList】

 

public class ArrayList<E> extends AbstractList<E> implements List<E>, RandomAccess, Cloneable, java.io.Serializable{

    private static final long serialVersionUID = 8683452581122892189L;
    private static final int DEFAULT_CAPACITY = 10;

　　public boolean add(E e) {
        ensureCapacityInternal(size + 1);  // Increments modCount!!
        elementData[size++] = e;
        return true;
    }

　　private void ensureCapacityInternal(int minCapacity) {
        ensureExplicitCapacity(calculateCapacity(elementData, minCapacity));
    }

　　private void ensureExplicitCapacity(int minCapacity) {
        modCount++;

        // overflow-conscious code
        if (minCapacity - elementData.length > 0)
            grow(minCapacity);
    }

　　private void grow(int minCapacity) {
        // overflow-conscious code
        int oldCapacity = elementData.length;
        int newCapacity = oldCapacity + (oldCapacity >> 1);
        if (newCapacity - minCapacity < 0)
            newCapacity = minCapacity;
        if (newCapacity - MAX_ARRAY_SIZE > 0)
            newCapacity = hugeCapacity(minCapacity);
        // minCapacity is usually close to size, so this is a win:
        elementData = Arrays.copyOf(elementData, newCapacity);
    }
　　

public int indexOf(Object o) {
    if (o == null) {
        for (int i = 0; i < size; i++)
            if (elementData[i]==null)
                return i;
    } else {
        for (int i = 0; i < size; i++)
            if (o.equals(elementData[i]))
                return i;
    }
    return -1;
}

public int lastIndexOf(Object o) {
    if (o == null) {
        for (int i = size-1; i >= 0; i--)
            if (elementData[i]==null)
                return i;
    } else {
        for (int i = size-1; i >= 0; i--)
            if (o.equals(elementData[i]))
                return i;
    }
    return -1;
}

}

 

　　　　初始容量：10　　　扩容：为原来的一半　int newCapacity = oldCapacity + (oldCapacity >> 1);

 

2、【HashMap】

public class HashMap<K,V> extends AbstractMap<K,V>
    implements Map<K,V>, Cloneable, Serializable {
    
   static final int DEFAULT_INITIAL_CAPACITY = 1 << 4;
   static final int MAXIMUM_CAPACITY = 1 << 30;  
   static final float DEFAULT_LOAD_FACTOR = 0.75f;

}

　　　　初始容量：16