按字母顺序从 ArrayList 返回元素

Question

我正在开发一个操作化学式的程序，我正在编写一个方法，该方法需要遍历一个名为“terms”的 ArrayList 并按字母顺序返回第一个。

例如terms = {Term('H',4),Term('C',2),Term('H',4),Term('C',1)} 将返回 Term('C',2)

到目前为止，我已经编写了这段代码，但它不起作用。我是 Java 语言的真正初学者。

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;
}

对于解决此问题的任何想法或建议，我将不胜感激。谢谢！

Answer 1

代码：

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 + "]";
    }       
}
 }

输出：

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 2

1- 你可以实现Comparable 并覆盖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;
}

然后使用

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;
    }

Answer 3

这是你需要做的：

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

你有两个选择：

1. 让您的Term 类实现Comparable 接口并覆盖其compareTo() 方法。然后您可以使用Collections.sort(listOfTerms) 对它们进行排序并循环。
2. 添加实现Comparator接口的类TermComparator，使用Collections.sort(listOfTerms, new TermComparator())并循环排序列表。

Answer 5

使用Collections.sort(terms);它将按字母顺序排列列表。