Java Comparator thenComparingDouble()用法及代码示例

Java中Comparator接口的thenComparingDouble(java.util.function.ToDoubleFunction)方法将返回字典顺序比较器，并带有提取双精度排序键的函数。如果要对比较方法中相等的那些值应用另一个比较，则在比较方法之后应用此方法。

用法:

default Comparator <T> thenComparingDouble(
    ToDoubleFunction <T> keyExtractor)

参数：此方法接受keyExtractor，该函数用于提取Double排序键。

返回值：此方法返回一个字典顺序比较器，由该字典比较器和Double排序键组成。

异常：如果参数为null，则此方法将引发NullPointerException。

以下示例程序旨在说明thenComparingDouble(java.util.function.ToDoubleFunction)方法：
示例1:

// Java program to demonstrate Comparator 
// thenComparingDouble(ToDoubleFunction) method 
  
import java.util.Arrays; 
import java.util.Collections; 
import java.util.Comparator; 
import java.util.List; 
  
public class GFG { 
  
    public static void main(String[] args) 
    { 
        List<Student> list = getStudentList(); 
  
        Comparator<Student> comparator 
            = Comparator 
                  .comparing(Student::getSchool) 
                  .thenComparingDouble(Student::getpercentageMarks); 
  
        Collections.sort(list, comparator); 
        System.out.println("After sort"); 
        list.forEach(s -> System.out.println(s)); 
    } 
  
    public static List<Student> getStudentList() 
    { 
  
        Student s1 = new Student("Ram", 85.5, "SJV"); 
        Student s2 = new Student("Shyam", 83.25, "MSH"); 
        Student s3 = new Student("Mohan", 86.55, "SJV"); 
        Student s4 = new Student("Sohan", 81.00, "MSH"); 
        Student s5 = new Student("Rabi", 55.6, "SJV"); 
        List<Student> list = Arrays.asList(s1, s2, s3, s4, s5); 
  
        return list; 
    } 
} 
  
class Student { 
  
    private String name; 
    private double percentageMarks; 
    private String school; 
  
    public Student(String name, 
                   double percentageMarks, 
                   String school) 
    { 
        this.name = name; 
        this.percentageMarks = percentageMarks; 
        this.school = school; 
    } 
  
    public String getName() 
    { 
        return name; 
    } 
  
    public void setName(String name) 
    { 
        this.name = name; 
    } 
  
    public double getpercentageMarks() 
    { 
        return percentageMarks; 
    } 
  
    public void setpercentageMarks(int percentageMarks) 
    { 
        this.percentageMarks = percentageMarks; 
    } 
  
    public String getSchool() 
    { 
        return school; 
    } 
  
    public void setSchool(String school) 
    { 
        this.school = school; 
    } 
  
    @Override
    public String toString() 
    { 
        return "Student [name=" + name + ",  
            percentageMarks 
            = " + percentageMarks  
              + ", school=" + school + "]"; 
    } 
}

IDE的控制台上打印的输出如下所示。
输出：

您可以在示例中看到，首先对学校进行排序，如果学校相同，则对百分比进行明智排序。

示例2:

// Java program to demonstrate Comparator 
// thenComparingDouble(ToDoubleFunction)  method 
  
import java.util.Arrays; 
import java.util.Comparator; 
import java.util.List; 
  
public class GFG { 
  
    public static void main(String... args) 
    { 
  
        List<Integer> list 
            = Arrays.asList(1, 2, 3, 4, 5, 6); 
  
        try { 
  
            // apply thenComparingDouble 
            Comparator.comparing(list::get) 
                .thenComparingDouble(null); 
        } 
        catch (Exception e) { 
  
            System.out.printf("Exception:" + e); 
        } 
    } 
}

控制台上打印的输出如下所示。
输出：

参考文献： https://docs.oracle.com/javase/10/docs/api/java/util/Comparator.html#thenComparingDouble(java.util.function.ToDoubleFunction)()

相关用法

注：本文由纯净天空筛选整理自AmanSingh2210大神的英文原创作品 Comparator thenComparingDouble() 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。