集合类binarySearch()方法 (Collections Class binarySearch() method)

Syntax:

句法：

    public static int binarySearch(List l, Type key_ele);
public static int binarySearch(List l, Type key_ele, Comparator com);

• binarySearch() method is available in java.util package.

  binarySearch()方法在java.util包中可用。

• binarySearch(List l, Type key_ele) method is used to find the given object (key_ele) in the given list (l) with the help of binary search.

  binarySearch(List l，Type key_ele)方法用于在二进制搜索的帮助下在给定列表(l)中找到给定对象(key_ele)。

• binarySearch(List l, Type key_ele, Comparator com) method is used to find the given object (key_ele) in the given list (l) and the list must be sorted based on defined Comparator object.

  binarySearch(List l，Type key_ele，Comparator com)方法用于在给定列表(l)中查找给定对象(key_ele)，并且必须基于定义的Comparator对象对列表进行排序。

• These methods may throw an exception at the time of finding the given element.

  这些方法在查找给定元素时可能会引发异常。

  ClassCastException: This exception may throw when the given parameter List elements that are mutually incomparable.

  ClassCastException ：当给定的参数List元素彼此不可比较时，可能引发此异常。

• These are static methods and it is accessible with the class name and if we try to access these methods with the class object then also we will not get any error.

  这些是静态方法，可以使用类名进行访问，如果尝试使用类对象访问这些方法，则也不会出现任何错误。

Parameter(s):

参数：

• In the first case, "binarySearch(List l, Type key_ele)"

  在第一种情况下，“ binarySearch(List l，Type key_ele)”

  • List l – represents the list object.
  • 列表l –表示列表对象。
  • Type key_ele – represents the key element to be searched.
  • key_ele类型 –表示要搜索的关键元素。

• In the second case, "binarySearch(List l, Type key_ele, Comparator com)"

  在第二种情况下，“ binarySearch(List l，Type key_ele，Comparator com)”

  • List l – represents the list object.
  • 列表l –表示列表对象。
  • Type key_ele – represents the key element to be searched.
  • key_ele类型 –表示要搜索的关键元素。
  • Comparator com – represents the Comparator object and we set the value to null that means it is natural or default order.
  • Comparator com –表示Comparator对象，我们将值设置为null表示它是自然顺序或默认顺序。

Return value:

返回值：

In both the cases, the return type of the method is int, it returns the position of the given key_ele(key element) when it exists in the given list.

在这两种情况下，该方法的返回类型均为int ，当它存在于给定列表中时，它将返回给定key_ele(key元素)的位置。

Example:

例：

// Java program to demonstrate the example 
// of binarySearch() method of Collections
import java.util.*;
public class BinarySearchOfCollections {
public static void main(String args[]) {
// Instantiates an array list object
List < Integer > arr_l = new ArrayList < Integer > ();
// By using add() method is to add
// objects in an array list
arr_l.add(20);
arr_l.add(10);
arr_l.add(40);
arr_l.add(30);
arr_l.add(50);
// Display ArrayList
System.out.println("ArrayList: " + arr_l);
// By using binarySearch(arr_l,30,null) method is
// to search the the given object 30 in an arr_l
// based on defined comparator object (null) and
// here we are using null so list must be sorted
// in an ascending order
int indices = Collections.binarySearch(arr_l, 30, null);
// Display indices
System.out.println("Collections.binarySearch(arr_l,30,null): " + indices);
// By using binarySearch(arr_l,30) method is
// to search the the given object 30 in an arr_l
// so list must be sorted in an natural or ascending order
indices = Collections.binarySearch(arr_l, 30);
// Display indices
System.out.println("Collections.binarySearch(arr_l,30): " + indices);
}
}

Output

输出量

ArrayList: [20, 10, 40, 30, 50]
Collections.binarySearch(arr_l,30,null): -3
Collections.binarySearch(arr_l,30): -3

翻译自: https://www.includehelp.com/java/collections-binarysearch-method-with-example.aspx