Generics, Collection Help: Sorty Object based on Name

[Mayu Mayooresan]

I'm trying to sort objects based on the name. I don't know where Im going wrong. Code seems understandable and legal to me but keep on getting the error "The constructor SortMe.Man() is undefined" on top of New Man().

import java.util.*;

public class SortMe{
	public static void main(String args[]){
		ArrayList<Man> list = new ArrayList<Man>();
		
		Man m1 = new Man();
		m1.Name = "mayoo";
		
		Man m2 = new Man();
		m2.Name = "Kugan";
		
		Man m3 = new Man();
		m3.Name = "Tharsan";
		
		list.add(m1);
		list.add(m2);
		list.add(m3);
		
		System.out.println(list);
		
		Collections.sort(list);
		
		System.out.println(list);
		
	}
	
	class Man implements Comparable<Man>{
		public String Name;
		
		public Man(String name) {
			this.Name = name;
			}

		public int compareTo(Man O) {
			Man m = (Man)O;
			
			return Name.compareTo(m.Name);
		}
	}
}

Thanks in advance.

[Henry Wong]

Mayu Mayooresan wrote: but keep on getting the error "The constructor SortMe.Man() is undefined" on top of New Man().

Basically, the compiler is complaining that you Man class doesn't have a constructor that takes no parameters. And if you take a quick look, your compiler is correct.

Henry

[Mayu Mayooresan]

Henry Wong wrote:

Mayu Mayooresan wrote: but keep on getting the error "The constructor SortMe.Man() is undefined" on top of New Man().

Basically, the compiler is complaining that you Man class doesn't have a constructor that takes no parameters. And if you take a quick look, your compiler is correct.

Henry

I made a empty constructor as below but now getting another error "No enclosing instance of type SortMe is accessible. Must qualify the allocation with an enclosing instance of type SortMe (e.g. x.new A() where x is an instance of SortMe)."

public Man(){
			
		}

I removed the constructor so it'll use the default constructor. now getting this same error as above ( awwwwwwww

import java.util.*;

public class SortMe{
	public static void main(String args[]){
		ArrayList<Man> list = new ArrayList<Man>();
		
		Man m1 = new Man();
		m1.Name = "mayoo";
		
		Man m2 = new Man();
		m2.Name = "Kugan";
		
		Man m3 = new Man();
		m3.Name = "Tharsan";
		
		list.add(m1);
		list.add(m2);
		list.add(m3);
		
		System.out.println(list);
		
		Collections.sort(list);
		
		System.out.println(list);
		
	}
	
	class Man implements Comparable<Man>{
		public String Name;
		
		public int compareTo(Man O) {
			Man m = (Man)O;
			
			return Name.compareTo(m.Name);
		}
	}
}

[Abhay Agarwal]

error is coming because of wrong inner class instantiation

Correct Code would be

public class SortMe {



 public static void main(String args[]){
        ArrayList<Man> list = new ArrayList<Man>();

        SortMe so = new SortMe();
        SortMe.Man m1 = so.new Man();
        m1.Name = "mayoo";

        SortMe.Man m2 = so.new Man();        //Man m2 = new Man();
        m2.Name = "Kugan";

       SortMe.Man m3 = so.new Man();         //Man m3 = new Man();
        m3.Name = "Tharsan";

        list.add(m1);
        list.add(m2);
        list.add(m3);

        System.out.println( list);

        Collections.sort(list);

        System.out.println(list);

    }

 class Man implements Comparable<Man>{
        public String Name;
       

        public int compareTo(Man O) {
            Man m = (Man)O;

            return Name.compareTo(m.Name);
        }
    }
   
}

Note the instatnitation code of m1, m2 and m3 object. Class Man is innner class to SortMe class. Rest of your code is fine.
You can read below mentioned link for more details about instantiation code syntax
http://download.oracle.com/javase/tutorial/java/javaOO/nested.html



If you move class Man out of SortMe class (as shown in below code) then your previous code within main method of SortMe would work fine

public class SortMe {

 public static void main(String args[]){
        ArrayList<Man> list = new ArrayList<Man>();
        Man m1 = new Man();
        m1.Name = "mayoo";

        Man m2 = new Man();
        m2.Name = "Kugan";

         Man m3 = new Man();
        m3.Name = "Tharsan";

        list.add(m1);
        list.add(m2);
        list.add(m3);

        System.out.println( list);

        Collections.sort(list);

        System.out.println(list);

    }

 
}

// class Man outside of class SortMe
class Man implements Comparable<Man>{
        public String Name;


        public int compareTo(Man O) {
            Man m = (Man)O;

            return Name.compareTo(m.Name);
        }
 }

Output of this code is

[javaapplication1.Man@19821f, javaapplication1.Man@addbf1, javaapplication1.Man@42e816]
[javaapplication1.Man@addbf1, javaapplication1.Man@42e816, javaapplication1.Man@19821f]

Hope I have cleared your doubt

Just a note that you can override toString() method of Man class to get better display of ArrayList contents (man objects)

[Mayu Mayooresan]

Thanks a lot

Now I understand where I went wrong. I wrote the Man class inside the SortMe class and trying to code the rest thinking that Man Class is outside SortMe class

Yeah I tried to overide toString also and it worked like magic.

Thanks a lot again and again for your valuable time.

Cheers.