Sorting in List<Hash Map>

[Vass Lee]

Hi All ,
I i have the data in below format:

Name Age Skill Company
Vass 21 Java Zylog
Samy 24 PB HP
Lee 18 ADF CTS
Reng 16 Java Info


I converted this data into java collections List<Hash Map> like this.

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
 
public class HashMapDemo {
    public static void main(String[] args) {
        // Create a hash map
        
        List<HashMap> list = new ArrayList<HashMap>();
        
        HashMap hm = new HashMap();
        hm.put("Name", new String("Vass"));
        hm.put("Age", new Integer(21));
        hm.put("Company", new String("Zylog"));
        hm.put("skill", new String("Java"));
        list.add(hm);
        
        HashMap hm1 = new HashMap();
        hm1.put("Name", new String("Samy"));
        hm1.put("Age", new Integer(24));
        hm1.put("Company", new String("HP"));
        hm1.put("skill", new String("PB"));
        list.add(hm1);
        
        HashMap hm2 = new HashMap();
        hm2.put("Name", new String("Lee"));
        hm2.put("Age", new Integer(18));
        hm2.put("Company", new String("CTS"));
        hm2.put("skill", new String("ADF"));
        list.add(hm2);
        
        HashMap hm3 = new HashMap();
        hm3.put("Name", new String("Reng"));
        hm3.put("Age", new Integer(16));
        hm3.put("Company", new String("Info"));
        hm3.put("skill", new String("Java"));
        list.add(hm3);
        
        
        Iterator i = list.iterator();
        while (i.hasNext()) {
            System.out.println(i.next());
        }
 
    }
}

As per data (table format) i want to sort the data in Column level
how can i to achieve ?.

List<HashMap> is type of collection is help to me?

Any idea?

Thanks,
Vass Lee

[Winston Gutkowski]

Vass Lee wrote:As per data (table format) i want to sort the data in Column level

List<HashMap> is type of collection is help to me?

You'd be much better off creating a class to hold that data (Person?) and then just creating a List<Person>. If you make your Person class Comparable, you can just sort it as is; otherwise one of the Collections.sort() methods also takes a Comparator.

Winston

[Vass Lee]

Hi Winston,

Thanks for your reply. Can you provide any sample for Creating Person class and how to hold the data in that class.?

I am new guy in java

Thanks,
Vass Lee,

[Nomaan Butt]

as winston suggested, make a Person class like below

class Person implements Comparable<Person>{

	String name,age,skill,company;
	Person(String name,String age,String skill,String company){
		this.name=name;
		this.age=age;
		this.skill=skill;
		this.company=company;
	}
	public int compareTo(Person o) {
		
		return this.name.compareTo(o.name);
			
	}
	
	@Override
	public String toString(){
		
		return "Name="+this.name+", Age="+this.age+" skill="+this.skill+" Comapny="+this.company;
	}
	
	
}

and create a list of type Person and add objects to it like this

List<Person> listPerson = new ArrayList<Person>();
        listPerson.add(new Person("Vass","21","Zylog","Java"));
        listPerson.add(new Person("Samy","24","PB","HP"));
        listPerson.add(new Person("Lee","18","ADF","CTS"));
        listPerson.add(new Person("Reng","16","Java","Info"));
        Collections.sort(listPerson);
        Iterator ia = listPerson.iterator();
        while (ia.hasNext()) {   
            System.out.println(ia.next().toString());   
        }

you can change the compareTo() method according to your need
hope this may help you.

[Winston Gutkowski]

Nomaan Butt wrote:make a Person class like below

@Vass: the only slight change I'd make to Nomaan's suggestion is not to use Strings for everything. 'Age' is plainly a numeric value, so make it one, viz:

class Person implements Comparable<Person> {
   String name;
   int age
   String skill;
   String company;

   Person(String name, String age, String skill, String company) {
      this.name = name;
      this.age = Integer.parseInt(age);
      this.skill = skill;
      this.company = company;
   }
   ...
}

and I suspect you'll also discover that something like "skill" is actually a code that is stored elsewhere in your database. If it is, then make it a class (or an enum) too. If not, forget what I said and just use a String.

HIH

Winston

[Vass Lee]

Hi Winston,

Thanks for your reply.Now i want to apply some filters in column level .how can i apply filter in person class? any filter method is there in java.util. package? can you provide any sample here ?

Thanks,
Vass Lee

[John Jai]

Now i want to apply some filters in column level .how can i apply filter in person class?

What do you mean by column level? Nomaan's code shows how to sort based on the variable name.... You want to do any more addition to the compareTo() method?

[Vass Lee]

Hi John,

Thanks for your reply.As per Nomaan's i can able to sort the variable level.Now i want filter the records in variable level.

Thanks,
Vass Lee

[John Jai]

Sorry Vass - i am not understanding what do you mean by filtering...

Might be you want to iterate the List<Person> and take a particular person object if the name variable has a particular value (say "Vass"?)

[Rob Spoor]

Create a java.util.Comparator<Person> implementation for all the specific ways you want to compare the Person objects.

[Winston Gutkowski]

Vass Lee wrote:Thanks for your reply.Now i want to apply some filters in column level .how can i apply filter in person class? any filter method is there in java.util. package? can you provide any sample here ?

Just a small point: you're in Java now and you have a class, so it's best not to think in terms of "columns" any more. Databases have columns, Java has fields (or attributes). Assuming that, per Nomaan's example, you have a java.util.List of Persons, a filtering method might look something like this:

public List<Person> namesStartingWith(List<Person> people, char firstLetter) {
   List<Person> filtered = new ArrayList<Person>(people.size());
   for (Person p : people) {
      if (p.getName().charAt(0) == firstLetter)
         filtered.add(p);
   }
   return filtered;
}

however, filters and sorts being what they are, there are endless possibilities (and you might even want to combine the two), so as the others say you should probably look at java.lang.Comparable and java.util.Comparator as well.

Also, Java has a dizzying array of collection types, some of which are very powerful, so I suggest you have a look at the tutorials and get familiar with them.

HIH

Winston