1.Stack is a subclass of Vector, which is a first-in-last-out (FILO) data structure. Stack inherits all the methods of Vector, and then extends five methods of its own: pop(), push(), peek() , empty(), search().
public Stack(): The no-argument constructor for stack.
synchronized E pop(): remove the object on top of the stack and return it as the value of this function
synchronized E peek(): View the top object on the stack, but do not remove it
push(E item): push the object onto the stack
synchronized empty(): determine whether the stack is empty
synchronized int search(Object o): returns the position of the object on the stack, in 1-bit base
It can be seen that pop, peek and search are synchronized, because the internal methods of empty and push call Vector's methods, and Vector is thread-safe.
2. Because Stack inherits Vector, let's see
Source code: protected Object[] elementData;
protected int elementCount
protected int capacityIncrement
private static final int MAX_ARRAY_SIZE = 2147483639
2.1 public E push(E item)
// push an item to the top of the stack
public E push(E item) {
//Call the method of adding elements in the Vector class
addElement(item);
return item;
}
public synchronized void addElement(E obj) {
// Implement the Fail-Fast mechanism by recording the modCount parameter
modCount++;
//Ensure that the size of the stack will not overflow the newly added data
ensureCapacityHelper(elementCount + 1);
elementData[elementCount++] = obj;
}
private void ensureCapacityHelper(int minCapacity) {
// Prevent overflow. Exceeds the length that the array can hold and needs to be dynamically expanded! ! !
if (minCapacity - elementData.length > 0)
grow(minCapacity);
}
//The key to the dynamic increase of the array is
private void grow(int minCapacity) {
// overflow-conscious code
int oldCapacity = elementData.length;
//If it is a Stack, the array expands to twice the original size
int newCapacity = oldCapacity + ((capacityIncrement > 0) ?
capacityIncrement : oldCapacity);
//After expanding the array, you need to judge twice
//The first time is whether the capacity of the new array is smaller than elementCount + 1 (minCapacity;)
if (newCapacity - minCapacity < 0)
newCapacity = minCapacity;
//The first time is whether the capacity of the new array is larger than the specified maximum limit Integer.MAX_VALUE - 8
//If it is large, the minCapacity is too large and needs to be judged
if (newCapacity - MAX_ARRAY_SIZE > 0)
newCapacity = hugeCapacity(minCapacity);
elementData = Arrays.copyOf(elementData, newCapacity);
}
//Check if the int value of the capacity has overflowed
private static int hugeCapacity(int minCapacity) {
if (minCapacity < 0) // overflow
throw new OutOfMemoryError();
return (minCapacity > MAX_ARRAY_SIZE) ?
Integer.MAX_VALUE :
MAX_ARRAY_SIZE;
}
2.2.public synchronized E peek();
// Find the object on top of the stack without removing it from the stack.
public synchronized E peek() {
int len = size();
if (len == 0)
throw new EmptyStackException();
return elementAt(len - 1);
}
//The method in Vector gets the number of elements in the actual stack
public synchronized int size() {
return elementCount;
}
public synchronized E elementAt(int index) {
if (index >= elementCount) {
//Array subscript out of bounds exception
throw new ArrayIndexOutOfBoundsException(index + " >= " + elementCount);
}
//Return the value of the data subscripted as index
return elementData(index);
}
@SuppressWarnings("unchecked")
E elementData(int index) {
return (E) elementData[index];
}
2.3.public synchronized E pop()
//Remove the object at the top of the stack and return the object as a function value
public synchronized E pop() {
E obj;
int len = size();
obj = peek();
//The value of len-1 is the index of the last number in the array
removeElementAt (len - 1);
return obj;
}
//Method in Vector
public synchronized void removeElementAt(int index) {
modCount++;
/ / Array subscript out of bounds exception occurs
if (index >= elementCount) {
throw new ArrayIndexOutOfBoundsException(index + " >= " + elementCount);
} else if (index < 0) {
throw new ArrayIndexOutOfBoundsException(index);
}
//The number of elements after index in the array, because of the method called by Stack, j is always 0
int j = elementCount - index - 1;
if (j > 0) {
// The elements after index in the array are moved forward as a whole (this method is very useful!!)
System.arraycopy(elementData, index + 1, elementData, index, j);
}
elementCount--;
elementData[elementCount] = null; /* to let gc do its work */
}
2.4.public boolean empty()
public boolean empty() {
return size() == 0;
}
2.5
// Return the position of the object on the stack, starting at 1. If the object o exists as an item on the stack, the method returns the closest distance to the top of the stack.
//The topmost item in the stack is considered to have a distance of 1.
public synchronized int search(Object o) {
//lastIndexOf returns the last occurrence of a specified string value,
//Search from back to front at a specified position in a string
int i = lastIndexOf(o);
if (i >= 0) {
//So the distance from the top of the stack needs to be subtracted
return size() - i;
}
return -1;
}
//Method in Vector
public synchronized int lastIndexOf(Object o) {
return lastIndexOf(o, elementCount-1);
}
public synchronized int lastIndexOf(Object o, int index) {
if (index >= elementCount)
throw new IndexOutOfBoundsException(index + " >= "+ elementCount);
//Null data can be placed in Vector and Stack
if (o == null) {
for (int i = index; i >= 0; i--)
if (elementData[i]==null)
return i;
} else {
for (int i = index; i >= 0; i--)
if (o.equals(elementData[i]))
return i;
}
return -1;
}