在对象中实现二进制搜索

在对象中实现二进制搜索

Java教程的对象排序文章中有一个示例，您可以编写自己的示例

Comparator

以对自定义类型进行比较。

然后，

ArrayList

（或任何其他

List

），要查找的键以及

Comparator

可以一起传递到

Collections.binarySearch

方法中。

这是一个例子：

import java.util.*;class BinarySearchWithComparator{  public static void main(String[] args)  {    // Please scroll down to see 'User' class implementation.    List<User> l = new ArrayList<User>();    l.add(new User(10, "A"));    l.add(new User(20, "B"));    l.add(new User(30, "C"));    Comparator<User> c = new Comparator<User>() {      public int compare(User u1, User u2) {        return u1.getId().compareTo(u2.getId());      }    };    // Must pass in an object of type 'User' as the key.    // The key is an 'User' with the 'id' which is been searched for.    // The 'name' field is not used in the comparison for the binary search,    // so it can be a dummy value -- here it is omitted with a null.    //    // Also note that the List must be sorted before running binarySearch,    // in this case, the list is already sorted.    int index = Collections.binarySearch(l, new User(20, null), c);    System.out.println(index);    // Output: 1    index = Collections.binarySearch(l, new User(10, null), c);    System.out.println(index);    // Output: 0    index = Collections.binarySearch(l, new User(42, null), c);    System.out.println(index);    // Output: -4 // See javadoc for meaning of return value.  }}class User {  private int id;  private String name;  public User(int id, String name) {    this.id = id;    this.name = name;  }  public Integer getId() {    return Integer.valueOf(id);  }}