Integer string compare to string in Java

Question

I have declared a class implementing comparable interface and compareTo method comparing two employees using employee id. Created class objects inserted into array list. Now When I use Collections.sort(arrayList Object) it is working fine.I have a confusion in how the comparison differs between comparable and comparator interface.I want to know how comparison happens between a employee id string which purely consists of numbers and other string employee id which has few characters and numbers using both the inerface.

class Velraj implements Comparable<Velraj>{

    String id;
    String work;

    public Velraj(String id, String work){

        this.id = id;
        this.work = work;
    }
    public String getId() {
        return id;
    }
    public void setId(String id) {
        this.id = id;
    }
    public String getWork() {
        return work;
    }
    public void setWork(String work) {
        this.work = work;
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((id == null) ? 0 : id.hashCode());
        result = prime * result + ((work == null) ? 0 : work.hashCode());
        return result;
    }
    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Velraj other = (Velraj) obj;
        if (id == null) {
            if (other.id != null)
                return false;
        } else if (!id.equals(other.id))
            return false;
        if (work == null) {
            if (other.work != null)
                return false;
        } else if (!work.equals(other.work))
            return false;
        return true;
    }
    public int compareTo(Velraj o) {
        // TODO Auto-generated method stub
        return this.getWork().compareTo(o.getWork());
    }


}

public class AppMain {

    public static void main(String[] args) {


        Velraj v1 = new Velraj("16450","Security Specialist");
        Velraj v2 = new Velraj("245591","Consultant");
        Velraj v3 = new Velraj("RNJIV3664","Java Architecct");

        ArrayList<Velraj> a = new ArrayList<Velraj>();
        a.add(v1);
        a.add(v2);
        a.add(v3);

       Collections.sort(a);

       /*Collections.sort(a, new Comparator<Velraj>(){

    public int compare(Velraj o1, Velraj o2) {
        // TODO Auto-generated method stub
        return o1.getId().compareTo(o2.getId());
    }

   });*/

       for(Velraj v: a){

           System.out.println(v.getId() +"--> " +v.getWork()); 
       }
    }   
}

Output using comparable:
245591--> Consultant
RNJIV3664--> Java Architecct
16450--> System Security Specialist


Output using comparator:
16450--> System Security Specialist
245591--> Consultant
RNJIV3664--> Java Architecct

Henry · Accepted Answer · 2018-02-17 14:59:35Z

2

Comparison of Strings uses lexicographic order, also known as alphabetical order. That is, order by the first character, and if the first character is equal look at the second character and so on.

The individual characters are ordered according to their character code. Basically digits < upper case letters < lower case letters.

answered Feb 17, 2018 at 14:59

Henry

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curlyBraces · Accepted Answer · 2018-02-17 14:56:16Z

2

The reason you are getting different results when using Comparable and Comparator is because you are comparing on different properties in both cases!

In the overridden compareTo method of your class, you have specified that objects should be sorted based on the work property ofVelraj class. But in compare method in your main function, you have specified that objects be sorted on id field of Velraj. If you use the same property in both cases, then you'd have gotten identical result on sort.

answered Feb 17, 2018 at 14:56

curlyBraces

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