ArrayList
1.创建ArrayList list1 = new ArrayList();
默认创建了一个空的数组
private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};
public ArrayList() {
this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
}
2.执行 list1.add(1);
public boolean add(E e) {
ensureCapacityInternal(size + 1); // 确保数组容量,如果是空数组,那么就设置默认长度或是设置设置为数据的长度。如果非空数组,长度不够就进行扩容。
elementData[size++] = e; //新添加的对象进行赋值
return true;
}
private static final int DEFAULT_CAPACITY = 10; //默认长度为10
private void ensureCapacityInternal(int minCapacity) {
if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
}
ensureExplicitCapacity(minCapacity);//进行分配数组长度
}
private void ensureExplicitCapacity(int minCapacity) {
modCount++;
if (minCapacity - elementData.length > 0) //需要的长度大于当前数组的长度,就进行扩容
grow(minCapacity);
}
private void grow(int minCapacity) {
int oldCapacity = elementData.length;
int newCapacity = oldCapacity + (oldCapacity >> 1); //先扩容为当前数组的一半
if (newCapacity - minCapacity < 0) //如果还小于需要的数组长度,那么新数组的长度等于需要的长度
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);//进行数组的复制,创建一个新数组将旧数组的值复制到新数组中。
}
3.执行list1.addAll(list2);
public boolean addAll(Collection<? extends E> c) {
Object[] a = c.toArray(); //上来马上将类型转化成数组,然后其他的步骤跟add()基本相同
int numNew = a.length;
ensureCapacityInternal(size + numNew); // Increments modCount
System.arraycopy(a, 0, elementData, size, numNew);
size += numNew;
return numNew != 0;
}
4.list1.add(index,element) 指定的位置上,添加一个元素,这时候集合的长度会添加
public void add(int index, E element) {
if (index > size || index < 0)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
ensureCapacityInternal(size + 1); // Increments modCount!!
//下面进行数组的指定位置的复制,将elementData中的index位置开始的数据复制到当前数据的
index+1位置开始逐条复制。并最后将element赋值到index位置上
System.arraycopy(elementData, index, elementData, index + 1,
size - index);
elementData[index] = element;
size++;
}
5. list1.set(2,10); 这个方法是将索引为2的位置上的数据进行赋值,并返回被替换的数据。
public E set(int index, E element) {
if (index >= size)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
E oldValue = (E) elementData[index];
elementData[index] = element;
return oldValue;
}
6. list1.remove((Integer) 11);
//无非是进行遍历,然后删除数据
public boolean remove(Object o) {
if (o == null) {
for (int index = 0; index < size; index++)
if (elementData[index] == null) {
fastRemove(index);
return true;
}
} else {
for (int index = 0; index < size; index++)
if (o.equals(elementData[index])) {
fastRemove(index);
return true;
}
}
return false;
}
private void fastRemove(int index) {
modCount++;
int numMoved = size - index - 1;
if (numMoved > 0)
//还是将数组中从index+1处的数据开始复制到索引在index处。
System.arraycopy(elementData, index + 1, elementData, index,
numMoved);
elementData[--size] = null; //将最后一条数据清空
}
7.list1.indexOf(1) //进行遍历,找到元素,并返回索引
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;
8.list1.contains(-1)
public boolean contains(Object o) {
return indexOf(o) >= 0; //如果不为-1,证明找到数据,返回true
}
9.list1.remove(0)和直接remove对象的方法的区别,就只不用先找到数据的索引。
public E remove(int index) {
if (index >= size)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
modCount++;
E oldValue = (E) elementData[index];
int numMoved = size - index - 1;
if (numMoved > 0)
//删除某个索引的元素,仍然用的数组复制的方法
System.arraycopy(elementData, index + 1, elementData, index,
numMoved);
elementData[--size] = null; // clear to let GC do its work
return oldValue;
}
10.list1.get(0)
public E get(int index) {
if (index >= size)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
//直接取数组中的数据
return (E) elementData[index];
11.list1.toArray(); 其实就是数组的复制
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public Object[] toArray() {
return Arrays.copyOf(elementData, size);
}
public static <T> T[] copyOf(T[] original, int newLength) {
return (T[]) copyOf(original, newLength, original.getClass());
}
public static <T,U> T[] copyOf(U[] original, int newLength, Class<? extends T[]> newType) {
@SuppressWarnings("unchecked")
T[] copy = ((Object)newType == (Object)Object[].class)
? (T[]) new Object[newLength]
: (T[]) Array.newInstance(newType.getComponentType(), newLength);
System.arraycopy(original, 0, copy, 0,
Math.min(original.length, newLength));
return copy;
}
执行代码Iterator iterator = list1.iterator();
while (iterator.hasNext()){ Log.e("TAG", "iterator==="+iterator.next().toString()); iterator.remove(); } 在ArrayList中发现源码,iteraor就是一个对象,里面封装了索引。 private class Itr implements Iterator<E> { int cursor; // index of next element to return int lastRet = -1; // index of last element returned; -1 if no such int expectedModCount = modCount; public boolean hasNext() { return cursor < limit; //判断当前索引是否小于集合长度 } @SuppressWarnings("unchecked") public E next() { if (modCount != expectedModCount) throw new ConcurrentModificationException(); int i = cursor; if (i >= limit) throw new NoSuchElementException(); Object[] elementData = ArrayList.this.elementData; if (i >= elementData.length) throw new ConcurrentModificationException(); cursor = i + 1; return (E) elementData[lastRet = i];//在这取出数组中的数据,并且为lastRet赋值 } public void remove() { if (lastRet < 0) throw new IllegalStateException(); if (modCount != expectedModCount) throw new ConcurrentModificationException(); try { ArrayList.this.remove(lastRet); //根据在next()中的被赋值的lastRet,调用ArrayList中的根据索引删除的remove()方法,进行删除。因此如果调用remove() 必须先调用next() cursor = lastRet; lastRet = -1; expectedModCount = modCount; limit--; } catch (IndexOutOfBoundsException ex) { throw new ConcurrentModificationException(); } } @Override @SuppressWarnings("unchecked") public void forEachRemaining(Consumer<? super E> consumer) { Objects.requireNonNull(consumer); final int size = ArrayList.this.size; int i = cursor; if (i >= size) { return; } final Object[] elementData = ArrayList.this.elementData; if (i >= elementData.length) { throw new ConcurrentModificationException(); } while (i != size && modCount == expectedModCount) { consumer.accept((E) elementData[i++]); } // update once at end of iteration to reduce heap write traffic cursor = i; lastRet = i - 1; if (modCount != expectedModCount) throw new ConcurrentModificationException(); } }
13.List integers = list1.subList(1, 3);
for(Integer i:integers) {
Log.e("TAG", "integers==="+i);
}
public List<E> subList(int fromIndex, int toIndex) {
//检查是否越界
subListRangeCheck(fromIndex, toIndex, size);
//竟然创建了一个新的对象SubList,这个SubList相当于一个和ArrayList相同的类,里面有和ArrayList相同的方法
return new SubList(this, 0, fromIndex, toIndex);
}
//虽然我用了增强for循环,但实质还是调用了get()方法,但是发现,和ArrayList的区别就是,增加了偏移量,仍然维护了由于的数组