题目和要求：
In this question, you will write a linked list class, and use it to store all of the words contained in a text file.
You will write your linked list class in a file called LinkedList.java, which will contain BOTH the
LinkedList class and the Node class (only the LinkedList class is public).
You have been provided with a main program file called A4Test.java and a text file called
darwin.txt.
First, create a Node class. It should contain, as usual, a pointer to another node, and a String reference.
Write a constructor that sets the data being stored in the Node, and set its link to the next Node to null.
Write appropriate getters and setters as well.
Next, create your LinkedList class. As usual, it should contain a first (top) pointer to the first node in
the list. Additionally, create a last pointer to the last Node in the linked list (we’ll see why later). Add an
integer instance variable to keep track of the size (i.e. the number of words) in the linked list.
Create the following public methods:
• A null constructor that initializes the two Node pointers to null and the size to 0
• int size() that returns the size of the list.
• void append(String), which takes the given word and places it at the end of the list, not at
the beginning. Instead of performing a costly traversal of the linked list from the beginning
until the end is reached, use the last pointer instead, when appending a new item. Be mindful
of the case when the list is empty.
• A second constructor that takes a String parameter, which is the name of a file. The
constructor will attempt to read the file and add all the words in the file to the linked list (using
append). Use whitespace to separate the lines into words. In Java, the String literal
"\\p{Space}+" specifies one or more whitespace characters.
• String format(int width) that returns a String containing all the words in their original
order, formatted in lines that are width characters long, fully justified (i.e. the lines are aligned
on both the left and right sides). This is achieved by adding extra spaces between the words so
that the right side is aligned at width characters. In order to make the justification look
balanced, distribute the extra spaces throughout the line. Add the extra spaces left-to-right on
each second line, and right-to-left on the alternating lines. You may find it helpful to use two
private methods to perform these justification steps (though you are not required to do so). The
last line is not justified, since it may contain only a few words.
A4test code:
public class A4Test{
public static void main(String [] args){
String fileName = "darwin.txt";
System.out.println("This is A4Test.\n");
LinkedList myList = new LinkedList(fileName);
System.out.println(myList.format(80));
System.out.println(fileName + " contains " + myList.size() + " words.");
}// main
}// class A4Test
drawin.txt内容：
qwertyuiopasdfghjklzxcvbnm
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