Help with lists

[datreta]

Hello.

I'm new here and to programming in Java. I'm starting to have classes now and I need help with a project. What I'm asked to do is the following:

- The user is asked to write a sentence;
- From that sentence, each word needs to be placed in a node of a chained list (i don't know if this is the correct term);
- Then, I need a new list with the sentence from the list before but with the words in a reverse order (ex: I am noob -> noob am I).

Hope someone can help me because I don't even know where to start.

Thank you in advance.

Regards.

[JosAH]

A few tips: read the API documentation for String.split( ... ) method and all about the List< ... > interface.

kind regards,

Jos

[datreta]

Ok, after some documentation checking, I've come up with this. Can someone take a look if I'm on the right track? How can I see if both lists are ok?

import javax.swing.JOptionPane;

public class menu {
    public static int options() {
        int op;
        do {
            String a = "Menu"
                    + "\n1 - write a sentence"
                    + "\n2 - words in a reverse order"
                    + "\n3 - create an ordered bidirectional list with words that are not repeated"
                    + "\n4 - delete word"
                    + "\n5 - delete word between x and y"
                    + "\n6 - Move nodes"
                    + "\n7 - Copy nodes"
                    + "\n8 - print lists"
                    + "\n0 - exit";
            op = Integer.parseInt(JOptionPane.showInputDialog(a + "\nOption? (0 to 8)"));
        }
            while ((op < 0) || (op > 8));
            return op;
    }  

   public static void main(String[] args) {
        list A = new list();
        list B = new list();
        int option = opcoes();
        while (option != 0) {
            String sentence;
            switch (option) {
            case 1: {
                do
                    sentence = JOptionPane.showInputDialog("Input sentence: ");
                while (sentence.compareTo("") == 0);
                A.receivesentence(sentence);
                break;
            }
            
            case 2: {
                do
                    sentence = JOptionPane.showInputDialog("Input sentence: ");
                while (sentence.compareTo("") == 0);
                B.receivesentence2(sentence);
                break;
            }
            
            case 3: {
               
                break;
            }
}
        }
            
    }
}

import java.util.*;

public class list {
	
		private node head;
		
		
		public void receivesentence(String sentence){
			
			String [] words = sentence.split(" ");
			for (int i = 0; i < words.length-1; i++){
				this.insertordered(words[i]);
			}
				
		}
		
		
		public void receivesentence2(String sentence){
			
			String [] words = sentence.split(" ");
			for (int i = 0; i < words.length-1; i++){
				this.insertinverted(words[i]);
			}
				
		}
		
		public void insertordered(String word){
			
			node new=new node(word);
			
			node temp=head;
			
				while((temp.getnext()!=null)&&(temp.getnext().getword().compareTo(new.getword())<0)){
					temp=temp.getnext();			
				}
				
				new.setnext(temp.getnext());
				new.setprev(temp);
				
				temp.setnext(new);
					
		}
	
		public void insertinverted(String word){
			
			node new=new node(word);
			
			node temp=head;
			
				while((temp.getnext()!=null)&&(temp.getnext().getword().compareTo(new.getword())>0)){
					temp=temp.getnext();			
				}
				
				new.setnext(temp.getnext());
				new.setprev(temp);
				
				temp.setnext(new);
					
		}	
		
	
		public String print()
		{
			String st = "";
			if (head.getnext() != head)
			{
				node temp = head.getnext();
				while(temp != head)
				{
					st += temp.getword() + " ";
					temp = temp.getnext();
				}
			}
			else
				st += "The list is empty!";
			
			return st;
		}
}

public class node {
	
	private String word;
	private node next;
	private node prev;
	
	public node(String word){
		this.word=word;
	}
		
	public String getword() {
		return word;
	}
	public void setword(String word) {
		this.word = word;
	}
	public node getnext() {
		return next;
	}
	public void setnext(node next) {
		this.next = next;
	}
	public node getprev() {
		return prev;
	}
	public void setprev(node prev) {
		this.prev = prev;
	}
	
	
}

[datreta]

Good morning.

Can someone help me with this one? It's due today... :o

[JosAH]

Good morning.

Can someone help me with this one? It's due today... :o

Did you give it a try? Does it compile? Does it run?

kind regards,

Jos

[j2me64]

some points i found while i try to compile the code:

• since new is a java keyword you can't use it as an identifier. change this identifier.

• when you call the method insertordered the variable temp is still null, so you get an NullPointerException. adapt the code to verify if temp is null.

i can make some semantic checks when the code is compilable.

[datreta]

Thank you for your answers.

I changed the code like you said (I think) and it does compile. However, when I type a sentence, eclipse gives me the following errors:

Exception in thread "main" java.lang.NullPointerException
	at pack.list.insertordered(list.java:39)
	at pack.list.receivesentence(list.java:13)
	at pack.menu.main(menu.java:36)

The code in list is now as follows:

package pack;
import java.util.*;

public class list {
    
        private node head;
        
        
        public void receivesentence(String sentence){
            
            String [] words = sentence.split(" ");
            for (int i = 0; i < words.length-1; i++){
                this.insertordered(words[i]);
            }
                
        }
        
        
        public void receivesentence2(String sentence){
            
            String [] words = sentence.split(" ");
            for (int i = 0; i < words.length-1; i++){
                this.insertinverted(words[i]);
            }
                
        }
        
        public void insertordered(String word){
            
            node newnode=new node(word);
            
            node temp=head;
            	if (temp == null){
                while((temp.getnext()!=null)&&(temp.getnext().getword().compareTo(newnode.getword())<0)){
                    temp=temp.getnext();
                }
                }
                
                newnode.setnext(temp.getnext());
                newnode.setprev(temp);
                
                temp.setnext(newnode);
                    
        }
    
        public void insertinverted(String word){
            
            node newnode=new node(word);
            
            node temp=head;
            
                while((temp.getnext()!=null)&&(temp.getnext().getword().compareTo(newnode.getword())>0)){
                    temp=temp.getnext();            
                }
                
                newnode.setnext(temp.getnext());
                newnode.setprev(temp);
                
                temp.setnext(newnode);
                    
        }    
        
    
        public String print()
        {
            String st = "";
            if (head.getnext() != head)
            {
                node temp = head.getnext();
                while(temp != head)
                {
                    st += temp.getword() + " ";
                    temp = temp.getnext();
                }
            }
            else
                st += "The list is empty!";
            
            return st;
        }
}