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java对ArrayList排序代码示例

2019年07月22日  | 移动技术网IT编程  | 我要评论

不废话了，直接给大家贴代码了。

class term { 
  string str; 
  int id;  
  public term(string str, int id) { 
    this.str = str; 
    this.id = id; 
  } 
  public string tostring() { 
    return str+" "+id; 
  } 
} 
class sterm implements comparable{ 
  string str; 
  int id; 
  public sterm(string str, int id) { 
    this.str = str; 
    this.id = id; 
  } 
  public int compareto(object o) { 
    return ((sterm)o).id - id; 
  } 
  public string tostring() { 
    return str+" "+id; 
  } 
} 
//method1: explicit implements comparator 
class termcomparator implements comparator { 
  public int compare (object o1, object o2) { 
    return ((term)o1).id - ((term)o2).id; 
  } 
} 
public class t1 { 
  /** 
   * @param args 
   */ 
  public static void main(string[] args) { 
    // todo auto-generated method stub 
//   arraylist<integer> arr = new arraylist<integer>( arrays.aslist(3,1,3,7,8,0)); 
//    
//   collections.sort(arr, new comparator(){ 
//      
//     public int compare(object o1, object o2){ 
//       return new double((integer)o1).compareto(new double ((integer)o2)); 
//     } 
//   }); 
    //method1 
    list<term> ls = new arraylist<term>(); 
    ls.add(new term("a",1)); 
    ls.add(new term("b",5)); 
    ls.add(new term("c",2)); 
    ls.add(new term("d",2)); 
    ls.add(new term("e",3)); 
    ls.add(new term("f",0)); 
    collections.sort(ls, new termcomparator()); 
    system.out.println(ls);//[f 0, a 1, c 2, d 2, e 3, b 5] 
    //method2: anonymous implements 
    collections.sort(ls, new comparator(){ 
      public int compare(object o1, object o2){ 
        return ((term)o2).id - ((term)o1).id; 
      } 
    }); 
    system.out.println(ls);//[b 5, e 3, c 2, d 2, a 1, f 0] 
    //method3:instantiate a comparator template 
    comparator<term> termcmp = new comparator<term>() { 
      public int compare(term t1, term t2) { 
        return t1.id - t2.id; 
      } 
    }; 
    collections.sort(ls, termcmp); 
    system.out.println(ls);//[f 0, a 1, c 2, d 2, e 3, b 5] 
    //method4:element implements comparable 
    list<sterm> lss = new arraylist<sterm>(); 
    lss.add(new sterm("a",1)); 
    lss.add(new sterm("b",5)); 
    lss.add(new sterm("c",2)); 
    lss.add(new sterm("d",2)); 
    lss.add(new sterm("e",3)); 
    lss.add(new sterm("f",0)); 
    collections.sort(lss); 
    system.out.println(lss);//[b 5, e 3, c 2, d 2, a 1, f 0] 
  } 
}

prioriyqueue的用法和上述的排序类似，有三种方法：

class wordfreq implements comparable{ 
    public string wd; 
    public int freq; 
    public wordfreq(string wd, int freq) { 
      this.wd = wd; 
      this.freq = freq; 
    } 
    public int compareto(object o) { 
      return ((wordfreq)o).freq - freq; 
    } 
    public string tostring() { 
      return wd+" "+freq; 
    } 
  } 
public class testt { 
  public static void main(string[] args) { 
    // todo auto-generated method stub 
    priorityqueue<wordfreq> pq = new priorityqueue<wordfreq>(); 
    pq.offer(new wordfreq("aaa", 3)); 
    pq.offer(new wordfreq("bbb", 4)); 
    pq.offer(new wordfreq("ccc",1)); 
    while(pq.peek() != null) { 
      system.out.println(pq.poll()); 
    }//从大到小输出 
  } 
}

注意，

for (wordfreq wf : pq) {
system.out.println(wf);
}

并不保证遍历的有序

如果list<string> ls 进行排序的话，不需要写comparator, 因为string本身有compareto的实现。

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