Sorting an arraylist in Java language

Question

I have an arraylist set up. I have input instuctions set up too, so that the user can enter one string, then one integer, then one string (the first name, the age, and the last name).

I need to sort the arraylist by the last name. The code I have entered so far is all under the main method:-

public static void main(String[] args) {
Name Name[] = new Name[50];
int count = 0;

for (int i=0; i<50; i++)
  NewName[i] = new Name();

//ADD NEW TO ARRAYLIST NAME
String FName = JOptionPane.showInputDialog("first name");
int age = Integer.parseInt(JOptionPane.showInputDialog("age"));
String LName = JOptionPane.showInputDialog("last name");
          NewName[count] = new Name(FName, age, LName);
count = count++;
}

//ITEMS SORT BY LAST NAME
//CODE FOR SORT GOES HERE

There is convention to name variables from small letter in java. — Artsiom Anisimau
– Artsiom Anisimau, Commented Mar 13, 2010 at 17:40
You are using an array of Name objects, not actually using an ArrayList. — Anthony Forloney
– Anthony Forloney, Commented Mar 13, 2010 at 17:41
Sorting depends on the implementation of the Name object. I can only hint you about Arrays.sort, Collections.sort, and Comparator. — Pindatjuh
– Pindatjuh, Commented Mar 13, 2010 at 17:43
just as a side note: count = count++; will increase count by... 0, zero, nil, nought. count = ++count; would increase count by 1. count++; would increase count by 1. count += 1; would increase count by 1. — Tedil
– Tedil, Commented Mar 13, 2010 at 17:47
So this is not an arraylist? It's just an array? I have tried to use:- Arrays.sort(NewName); Collections.sort(NewName); And both do not work, the compiler fails... — Computeristic
– Computeristic, Commented Mar 13, 2010 at 17:49

saugata · Accepted Answer · 2010-03-14 04:41:45Z

5

Take a look at Comparable, Comparator, Arrays.sort and Collections.sort

import java.util.Arrays;


class Name implements Comparable<Name> {

    private String lastName;
    //Other fields

    public Name(String lastName){
        this.lastName = lastName;
    }

    public int compareTo(Name o) {
        //Null checks etc
        return lastName.compareTo(o.lastName);
    }
    public String getLastName(){
        return lastName;
    }
    //Getter and setter methods
}

public class Test{
    public static void main(String[] args) {
        Name[] arr = new Name[]{new Name("AAC"), new Name("AAD"), new Name("AAA"),new Name("ABC"), new Name("AADDE")};
        Arrays.sort(arr);
        for(Name nm:arr){
            System.out.println(nm.getLastName());
        }
    }
}

edited Mar 14, 2010 at 4:41

answered Mar 13, 2010 at 17:43

saugata

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3 Comments

helpermethod Over a year ago

The null checks are actually not required here (or when instanceof is used).

saugata Over a year ago

@Helper Method Are you referring to the compareTo method? Actually it is, the parameter could be null.

helpermethod Over a year ago

@sauguta Sry, you're right, I thought String's compareTo() method would do the null check.

helpermethod · Accepted Answer · 2010-03-13 17:58:40Z

4

This isn't meant to be offensive but I would suggest you learn the basics before you move on to Swing.

answered Mar 13, 2010 at 17:58

helpermethod

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1 Comment

Carl Over a year ago

I think Helper is suggesting arrays are the basics. I'd tend to agree.

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