Java ArrayList.add 的实现方法

 /** * Appends the specified element to the end of this list. * * @param e element to be appended to this list * @return true (as specified by {@link Collection#add}) */ public boolean add(E e) { ensureCapacityInternal(size + 1); // Increments modCount!! elementData[size++] = e; return true; }

 /** * Inserts the specified element at the specified position in this * list. Shifts the element currently at that position (if any) and * any subsequent elements to the right (adds one to their indices). * * @param index index at which the specified element is to be inserted * @param element element to be inserted * @throws IndexOutOfBoundsException {@inheritDoc} */ public void add(int index, E element) { rangeCheckForAdd(index); ensureCapacityInternal(size + 1); // Increments modCount!! System.arraycopy(elementData, index, elementData, index + 1, size - index); elementData[index] = element; size++; } 

 void ObjArrayKlass::copy_array(arrayOop s, int src_pos, arrayOop d, int dst_pos, int length, TRAPS) { assert(s->is_objArray(), "must be obj array"); if (!d->is_objArray()) { THROW(vmSymbols::java_lang_ArrayStoreException()); } // Check is all offsets and lengths are non negative if (src_pos <0 || dst_pos < 0 length 0) { throw(vmsymbols::java_lang_arrayindexoutofboundsexception()); }> (unsigned int) s->length()) || (((unsigned int) length + (unsigned int) dst_pos) > (unsigned int) d->length()) ) { THROW(vmSymbols::java_lang_ArrayIndexOutOfBoundsException()); } // Special case. Boundary cases must be checked first // This allows the following call: copy_array(s, s.length(), d.length(), 0). // This is correct, since the position is supposed to be an 'in between point', i.e., s.length(), // points to the right of the last element. if (length==0) { return; } if (UseCompressedOops) { narrowOop* const src = objArrayOop(s)->obj_at_addr(src_pos); narrowOop* const dst = objArrayOop(d)->obj_at_addr(dst_pos); do_copy(s, src, d, dst, length, CHECK); } else { oop* const src = objArrayOop(s)->obj_at_addr(src_pos); oop* const dst = objArrayOop(d)->obj_at_addr(dst_pos); do_copy (s, src, d, dst, length, CHECK); } } 

 // Either oop or narrowOop depending on UseCompressedOops. template  void ObjArrayKlass::do_copy(arrayOop s, T* src, arrayOop d, T* dst, int length, TRAPS) { BarrierSet* bs = Universe::heap()->barrier_set(); // For performance reasons, we assume we are that the write barrier we // are using has optimized modes for arrays of references. At least one // of the asserts below will fail if this is not the case. assert(bs->has_write_ref_array_opt(), "Barrier set must have ref array opt"); assert(bs->has_write_ref_array_pre_opt(), "For pre-barrier as well."); if (s == d) { // since source and destination are equal we do not need conversion checks. assert(length > 0, "sanity check"); bs->write_ref_array_pre(dst, length); Copy::conjoint_oops_atomic(src, dst, length); } else { // We have to make sure all elements conform to the destination array Klass* bound = ObjArrayKlass::cast(d->klass())->element_klass(); Klass* stype = ObjArrayKlass::cast(s->klass())->element_klass(); if (stype == bound || stype->is_subtype_of(bound)) { // elements are guaranteed to be subtypes, so no check necessary bs->write_ref_array_pre(dst, length); Copy::conjoint_oops_atomic(src, dst, length); } else { // slow case: need individual subtype checks // note: don't use obj_at_put below because it includes a redundant store check T* from = src; T* end = from + length; for (T* p = dst; from klass())->is_subtype_of(bound)) { bs->write_ref_field_pre(p, new_val); *p = element; } else { // We must do a barrier to cover the partial copy. const size_t pd = pointer_delta(p, dst, (size_t)heapOopSize); // pointer delta is scaled to number of elements (length field in // objArrayOop) which we assume is 32 bit. assert(pd == (size_t)(int)pd, "length field overflow"); bs->write_ref_array((HeapWord*)dst, pd); THROW(vmSymbols::java_lang_ArrayStoreException()); return; } } } } bs->write_ref_array((HeapWord*)dst, length); } 

 /** * Increases the capacity to ensure that it can hold at least the * number of elements specified by the minimum capacity argument. * * @param minCapacity the desired minimum capacity */ 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); }