从ArrayList按字母顺序返回元素

Question

I'm working on a program to manipulate chemical formulae, and I'm writing a method which needs to loop through an ArrayList called "terms" and return the first one alphabetically.

eg terms = {Term('H',4),Term('C',2),Term('H',4),Term('C',1)} would return Term('C',2)

I've written this code so far but it's not working. I'm a real beginner to the Java language.

public Term nextElement()
{
    int i = 0;
    for (i = 0; i < terms.size()-1; i++)
    {
        int j = 1;
        while (i + j <= terms.size())
        if (terms.get(i).getElement() > terms.get(i+j).getElement())
        {
            terms.remove(i+j++);
            return terms.get(i);
        }
    }
    return null;
}

I'd appreciate any ideas or suggestions to solve this problem. Thanks!

Answer 1

You have two options here:

1. Let your Term class implement Comparable interface and override its compareTo() method. Then you can use Collections.sort(listOfTerms) to sort them and loop through.
2. Add class TermComparator which implements Comparator interface, use Collections.sort(listOfTerms, new TermComparator()) and loops through the sorted list.

Answer 2

use Collections.sort(terms); it will arrange the list alphabetically.

Answer 3

This is what you need to do:

List<Term> terms = //your list
Collections.sort(terms, new Comparator<Term>() {
    @Override
    public int compare(Term t1, Term t2) {
        return t1.getElement().compareTo(t2.getElement());
    }
});

Answer 4

CODE:

public class CodeSample {


public static void main(String[] args) {
    List<Term> terms=new ArrayList<Term>();
    terms.add(new Term('H',4));
    terms.add(new Term('C',2));
    terms.add(new Term('H',4));
    terms.add(new Term('C',1));
    System.out.println("Before Sorting");
    for(Term term:terms){
        System.out.print(term.toString().concat(" "));
    }
    Collections.sort(terms,new Comparator<Term>() {
        @Override
        public int compare(Term object1, Term object2) {                
            if (object1.getElement() != object2.getElement()) {
                return object1.getElement() - object2.getElement();
            } else {
                return object2.getCount() - object1.getCount();
            }           
        }
    });
    //Sorted terms
    System.out.println("After Sorting");
    for(Term term:terms){
        System.out.print(term.toString().concat(" "));
    }
}

public static class Term{
    private char element;
    private int count;
    public Term(char element, int count) {
        super();
        this.element = element;
        this.count = count;
    }
    public char getElement() {
        return element;
    }
    public int getCount() {
        return count;
    }
    @Override
    public String toString() {
        return "Term [element=" + element + ", count=" + count + "]";
    }       
}
 }

OUTPUT:

Before Sorting
Term [element=H, count=4] Term [element=C, count=2] Term [element=H, count=4] Term [element=C, count=1] 
After Sorting
Term [element=C, count=2] Term [element=C, count=1] Term [element=H, count=4] Term [element=H, count=4] 

Answer 5

1- you can implement Comparable and override compareTo()

int compareTo(Object obj){
Term term = (Term)obj;
if(term.getElement < this.getElement())
  return 1;
else if (term.getElement == this.getElement())
  return 0;
else
  return -1;
}

then use

Collection.sort(terms);

2-

 public Term nextElement()
    {
        char minElement = 'Z';
        int index = 0;
        for (int i = 0; i < terms.size(); i++)
        {
            if (terms.get(i).getElement() < minElement)
            {
                minElement = terms.get(i).getElement();
                index = i;
            }
        }
        Term temp = terms.get(index);
        terms.remove(index)
        return temp;
    }