Java Stream.max()用法及代码示例

Stream.max()根据提供的Comparator返回流的最大元素。比较器是一种比较函数，它对某些对象集合施加总排序。 max()是一种终端操作，它组合流元素并返回摘要结果。因此，max()是归约的一种特殊情况。该方法返回Optional实例。

用法:

Optional<T> max(Comparator<? super T> comparator)

Where, Optional is a container object which
may or may not contain a non-null value 
and T is the type of objects
that may be compared by this comparator

异常：如果最大元素为null，则此方法引发NullPointerException。

示例1:

// Implementation of Stream.max() 
// to get the maximum element 
// of the Stream according to the 
// provided Comparator. 
import java.util.*; 
import java.util.Optional; 
import java.util.Comparator; 
  
class GFG { 
  
    // Driver code 
    public static void main(String[] args) 
    { 
  
        // Creating a list of integers 
        List<Integer> list = Arrays.asList(-9, -18, 0, 25, 4); 
  
        System.out.print("The maximum value is : "); 
  
        // Using stream.max() to get maximum 
        // element according to provided Comparator 
        // and storing in variable var 
        Integer var = list.stream().max(Integer::compare).get(); 
  
        System.out.print(var); 
    } 
}

输出：

The maximum value is : 25

示例2:

// Implementation of Stream.max() 
// to get the maximum element 
// of the Stream according to the 
// provided Comparator. 
import java.util.*; 
import java.util.Optional; 
import java.util.Comparator; 
  
class GFG { 
  
    // Driver code 
    public static void main(String[] args) 
    { 
  
        // Creating a list of integers 
        List<Integer> list = Arrays.asList(-9, -18, 0, 25, 4); 
  
        // Using stream.max() to get maximum 
        // element according to provided Comparator 
        // Here, the smallest element in list 
        // will be stored in variable var 
        Optional<Integer> var = list.stream() 
                     .max(Comparator.reverseOrder()); 
  
        // If a value is present, isPresent() 
        // will return true, else display message 
        if (var.isPresent()) { 
            System.out.println(var.get()); 
        } 
        else { 
            System.out.println("-1"); 
        } 
    } 
}

输出：

-18

示例3:

// Implementation of Stream.max() 
// to get the maximum element 
// of the Stream according to the 
// provided Comparator. 
import java.util.*; 
import java.util.Optional; 
import java.util.Comparator; 
  
class GFG { 
  
    // Driver code 
    public static void main(String[] args) 
    { 
  
        // Creating a list of Strings 
        List<String> list = Arrays.asList("G", "E", "E", "K", 
                                          "g", "e", "e", "k"); 
  
        // using Stream.max() method with Comparator 
        // Here, the character with maximum ASCII value 
        // is stored in variable MAX 
        String MAX = list.stream().max(Comparator. 
                       comparing(String::valueOf)).get(); 
  
        // Displaying the maximum element in 
        // the stream according to provided Comparator 
        System.out.println("Maximum element in the "
                           + "stream is : " + MAX); 
    } 
}

输出：

Maximum element in the stream is : k

示例4:

// Implementation of Stream.max() 
// to get the maximum element 
// of the Stream according to the 
// provided Comparator. 
import java.util.*; 
import java.util.Optional; 
import java.util.Comparator; 
  
class GFG { 
  
    // Driver code 
    public static void main(String[] args) 
    { 
  
        // creating an array of strings 
        String[] array = { "Geeks", "for", "GeeksforGeeks", 
                           "GeeksQuiz" }; 
  
        // Here, the Comparator compares the strings 
        // based on their last characters and returns 
        // the maximum value accordingly 
        // The result is stored in variable MAX 
        Optional<String> MAX = Arrays.stream(array).max((str1, str2) ->   
                       Character.compare(str1.charAt(str1.length() - 1),  
                                       str2.charAt(str2.length() - 1))); 
  
        // If a value is present, 
        // isPresent() will return true 
        if (MAX.isPresent())  
            System.out.println(MAX.get());         
        else 
            System.out.println("-1");         
    } 
}

输出：

GeeksQuiz

相关用法

注：本文由纯净天空筛选整理自Sahil_Bansall大神的英文原创作品 Stream.max() method in Java with Examples。非经特殊声明，原始代码版权归原作者所有，本译文未经允许或授权，请勿转载或复制。