public abstract class AbstractSequentialList<E> extends AbstractList<E>

public abstract class AbstractList<E> extends AbstractCollection<E> implements List<E>

Interface： List(public interface List<E> extends Collection<E> )
The <tt>List</tt> interface provides two methods to search for a specified  object.   
From a performance standpoint, these methods should be used with caution.      
In many implementations they will perform costly linear searches.    

Abstract class: AbstractList(public abstract class AbstractList<E> extends AbstractCollection<E> implements List<E>)  
To implement an unmodifiable list, the programmer needs only to extend this class and provide implementations for the {@link #get(int)} and {@link List#size() size()} methods.

To implement a modifiable list, the programmer must additionally override the {@link #set(int, Object) set(int, E)} method (which otherwise throws an {@code UnsupportedOperationException}).  If the list is variable-size the programmer must additionally override the {@link #add(int, Object) add(int, E)} and {@link #remove(int)} methods.


about---> Itr, ListItr, RandomAccessSubList <---------


class: ArrayList(public class ArrayList<E> extends AbstractList<E> implements List<E>, RandomAccess, Cloneable, java.io.Serializable)
transient Object[] elementData; // non-private to simplify nested class access

public final class String
    implements java.io.Serializable, Comparable<String>, CharSequence {
    /** The value is used for character storage. */
    private final char value[];

    /** Cache the hash code for the string */
    private int hash; // Default to 0

    public int hashCode() {
        int h = hash;
        if (h == 0 && value.length > 0) {
            char val[] = value;

            for (int i = 0; i < value.length; i++) {
                h = 31 * h + val[i];//32=2^5    左移5位减去自身+字符ASCII码值
            }
            hash = h;
        }
        return h;
    }
    public boolean equals(Object anObject) {
        if (this == anObject) {//同一个引用
            return true;
        }
        if (anObject instanceof String) {
            String anotherString = (String)anObject;
            int n = value.length;
            if (n == anotherString.value.length) {//长度相同（减少比较次数）
                char v1[] = value;
                char v2[] = anotherString.value;
                int i = 0;
                while (n-- != 0) {//。。。
                    if (v1[i] != v2[i])
                        return false;
                    i++;
                }
                return true;
            }
        }
        return false;
    }
}

static class AppClassLoader extends URLClassLoader
static class ExtClassLoader extends URLClassLoader

<tt>Class</tt> objects for array classes are not created by class loaders, but are created automatically as required by the Java runtime.    
The class loader for an array class, as returned by {@link Class#getClassLoader()} is the same as the class loader for its element type; if the element type is a primitive type, then the array class has no class loader.    

<p> The <tt>ClassLoader</tt> class uses a delegation model to search for classes and resources.  
Each instance of <tt>ClassLoader</tt> has an associated parent class loader.  
When requested to find a class or resource, a <tt>ClassLoader</tt> instance will delegate the search for the class or resource to its parent class loader
before attempting to find the class or resource itself.  
The virtual machine's built-in class loader, called the "bootstrap class loader", does not itself have a parent but may serve as the parent of a <tt>ClassLoader</tt> instance.