Java 中的 Stream.max()方法，示例
原文:https://www . geesforgeks . org/stream-max-method-Java-examples/
Stream.max()根据提供的比较器返回流的最大元素。比较器是一个比较函数，它对一些对象集合进行总排序。max()是一个终端操作，它组合流元素并返回一个汇总结果。所以，max()是归约的特例。该方法返回可选实例。
语法:
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:如果最大元素为空，该方法抛出 空指针异常 。
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
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
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
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
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