java二进制对象_java – 在对象中实现二进制搜索

Java教程的

Object Ordering文章有一个写自己的

Comparator的例子，以便对自定义类型进行比较。

然后，ArrayList(或任何其他List)，查找的关键字以及Comparator可以传递到Collections.binarySearch方法中。

以下是一个例子：

import java.util.*;

class BinarySearchWithComparator

{

public static void main(String[] args)

{

// Please scroll down to see User class implementation.

List l = new ArrayList();

l.add(new User(10, "A"));

l.add(new User(20, "B"));

l.add(new User(30, "C"));

Comparator c = new Comparator() {

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);

}

}

Java教程的 Object Ordering文章有一个写自己的 Comparator的例子，以便对自定义类型进行比较。 然后，ArrayList(或任何其他List)，查找的关键字以及Comparator可以传递到Collections.binarySearch方法中。 以下是一个例子： import java.util.*; class BinarySearchWithComparator { public static void main(String[] args) { // Please scroll down to see User class implementation. List l = new ArrayList(); l.add(new User(10, "A")); l.add(new User(20, "B")); l.add(new User(30, "C")); Comparator c = new Comparator() { 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); } }