Java Comparator comparingDouble()用法及代码示例

Java中Comparator接口的compareDouble(java.util.function.ToDoubleFunction)方法接受一个函数作为参数，该参数从类型T中提取一个双精度排序键，并返回一个与该排序键进行比较的Comparator。指定的函数也可以序列化。

用法:

static <T> Comparator<T> comparingDouble(
    ToDoubleFunction <T> keyExtractor)

参数：此方法接受单个参数keyExtractor，该函数用于提取双精度排序键。

返回值：此方法返回一个比较器，该比较器通过提取的键进行比较

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compareingDouble(java.util.function.ToDoubleFunction)方法：
示例1:

// Java program to demonstrate Comparator 
// comparingDouble(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) 
    { 
  
        // create some user objects 
        User u1 = new User("Aaman", 3500.56); 
        User u2 = new User("Joyita", 4222.99); 
        User u3 = new User("Suvam", 2832.34); 
        User u4 = new User("mahafuj", 2522.76); 
  
        // before sort 
        List<User> list = Arrays.asList(u2, u1, u4, u3); 
        System.out.println("Before Sort:"); 
        list.forEach(user -> System.out.println(user)); 
  
        Collections.sort(list, 
                         Comparator.comparingDouble(User::getSalary)); 
        System.out.println("\nAfterSort:"); 
        list.forEach(user -> System.out.println(user)); 
    } 
} 
  
class User implements Comparable<User> { 
    public String name; 
    public double salary; 
  
    public User(String name, double d) 
    { 
        this.name = name; 
        this.salary = d; 
    } 
  
    public int compareTo(User u1) 
    { 
        return name.compareTo(u1.name); 
    } 
  
    public String getName() 
    { 
        return name; 
    } 
  
    public void setName(String name) 
    { 
        this.name = name; 
    } 
  
    public double getSalary() 
    { 
        return salary; 
    } 
  
    public void setSalary(double salary) 
    { 
        this.salary = salary; 
    } 
  
    @Override
    public String toString() 
    { 
        return "User [name=" + name 
            + ", salary="
            + salary + "]"; 
    } 
}

IDE的控制台上打印的输出如下所示。
输出：

示例2:

// Java program to demonstrate Comparator 
// comparingDouble(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) 
    { 
  
        // before sort 
        List<Order> list = Arrays.asList( 
            new Order("A382y482y48", 32684.82), 
            new Order("Vvekhfbkje2", 28348.47), 
            new Order("efkhfbekjfbe", 47674.49), 
            new Order("bhdhdfaddvad", 78449.43), 
            new Order("abkasbcjabjc", 10104.43)); 
  
        System.out.println("Before Sort:"); 
        list.forEach(order -> System.out.println(order)); 
  
        Collections.sort(list, 
                         Comparator.comparingDouble(Order::getValue)); 
        System.out.println("\nAfter Sort:"); 
        list.forEach(order -> System.out.println(order)); 
    } 
} 
  
class Order implements Comparable<Order> { 
    public String orderNo; 
    public double value; 
  
    public int compareTo(Order o1) 
    { 
        return orderNo.compareTo(o1.orderNo); 
    } 
  
    public Order(String orderNo, double value) 
    { 
        super(); 
        this.orderNo = orderNo; 
        this.value = value; 
    } 
  
    @Override
    public String toString() 
    { 
        return "Order [orderNo=" + orderNo 
            + ", value=" + value + "]"; 
    } 
  
    public String getOrderNo() 
    { 
        return orderNo; 
    } 
  
    public void setOrderNo(String orderNo) 
    { 
        this.orderNo = orderNo; 
    } 
  
    public double getValue() 
    { 
        return value; 
    } 
  
    public void setValue(double value) 
    { 
        this.value = value; 
    } 
}

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#comparingDouble(java.util.function.ToDoubleFunction)

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