ArrayList

1. The structure of ArrayList

2. What is ArrayList?

• An ArrayList is a data structure that behaves like a computerarray but also implements the ability todynamically grow the size of the array as needed. ArrayList structure can grow and shrink the size of the array in response to the addition or deletion of elements.
• Using an ArrayList provides a program with the ability to access data objects with an index number instantly instead of having to walk through an entire sequence of data to find an address.
• ArrayList is not thread-safe, it is used in single thread.
  

3. The definition of ArrayList

java.lang.Object --> java.util.AbstractCollection<E> --> java.util.AbstractList<E>  --> java.util.ArrayList<E>

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

• ArrayList extends AbstractList and implements List.
• ArrayList implement RandomAccess(nothing), it support random access function.
• ArrayList implement Cloneable(Object.clone), it can be clone.
• ArrayList implement java.io.Serializable interface, which meansArrayList supportserialization.

4. Private property

private transient Object[] elementData;   // Array

private int size;         // The size of the ArrayList.

transient

• JVM life cycle            
• Java stream
  
• Java serialization

             When JVM in its life cycle, object exist. Java Serialization make the object can be stored  after JVM stop running.

• transient

• transient variable value can not be saved after object serilized.
• transient can only be used to restrict variable, not method and class. Local variable can not be defined as transient.
• static variable can not be serialized no matter it is transient or not.

 1 public class UserInfo implements Serializable {
 2     private static final long serialVersionUID = 996890129747019948L;
 3     private String name;
 4     private transient String psw;
 5 
 6     public UserInfo(String name, String psw) {
 7         this.name = name;
 8         this.psw = psw;
 9     }
10 
11     public String toString() {
12         return "name=" + name + ", psw=" + psw;
13     }
14 }
15 
16 public class TestTransient {
17     public static void main(String[] args) {
18         UserInfo userInfo = new UserInfo("Jone", "123456");
19         System.out.println(userInfo);
20         try {
21             // Serialization，transient property can not be serialized
22             ObjectOutputStream o = new ObjectOutputStream(new FileOutputStream(
23                     "UserInfo.out"));
24             o.writeObject(userInfo);
25             o.close();
26         } catch (Exception e) {
27             // TODO: handle exception
28             e.printStackTrace();
29         }
30         try {
31             // read UserInfo.out
32             ObjectInputStream in = new ObjectInputStream(new FileInputStream(
33                     "UserInfo.out"));
34             UserInfo readUserInfo = (UserInfo) in.readObject();
35             // read psw is null
36             System.out.println(readUserInfo.toString());
37         } catch (Exception e) {
38             // TODO: handle exception
39             e.printStackTrace();
40         }
41     }
42 }

5. Constructor in ArrayList

ArrayList() // 10

ArrayList(int capacity)

ArrayList(Collection<? extends E> collection)

6.  Arrays.copyof()  vs  System.arraycopy()

public static <T,U> T[] copyOf(U[] original, int newLength, Class<? extends T[]> newType) {                                                                                                                             
      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;                                                                                                                                                                                                                                                               
  }                                                                                                                                                                                                                                                                                      
 

Arrays.copyof() create a new Array with lengthnewLength, then callSystem.arraycopy(), copy the elements from the originalArrays to newArrays.

7. Functions in ArrayList

// Collection中定义的API
boolean             add(E object)
boolean             addAll(Collection<? extends E> collection)
void                     clear()
boolean             contains(Object object)
boolean             containsAll(Collection<?> collection)
boolean             equals(Object object)
int                        hashCode()
boolean             isEmpty()
Iterator<E>        iterator()
boolean             remove(Object object)
boolean             removeAll(Collection<?> collection)
boolean             retainAll(Collection<?> collection)
int                       size()
<T> T[]               toArray(T[] array)
Object[]              toArray()

// AbstractCollection中定义的API
void                add(int location, E object)
boolean        addAll(int location, Collection<? extends E> collection)
E                    get(int location)
int                  indexOf(Object object)
int                  lastIndexOf(Object object)
ListIterator<E>     listIterator(int location)
ListIterator<E>     listIterator()
E                   remove(int location)
E                   set(int location, E object)
List<E>        subList(int start, int end)

// ArrayList新增的API
Object             clone()
void                 ensureCapacity(int minimumCapacity)  // Every time add one element , the capacity will enlarge to (oldcapacity*3/2)+1
void                 trimToSize()
void                 removeRange(int fromIndex, int toIndex)