Java Comparator comparingDouble()方法及示例

Java 中比较器接口的 comparingDouble( java.util.function.ToDoubleFunction ) 方法接受一个函数作为参数，该函数从一个类型 T 中提取一个 double 排序键，并返回一个通过该排序键进行比较的比较器。如果指定的函数也是可序列化的，返回的比较器是可序列化的。

语法

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

参数： 该方法接受一个单参数 keyExtractor ，它是用来提取双排序键的函数。

返回值： 该方法返回一个比较器，通过提取的键进行比较。

异常： 如果参数为空，该方法会抛出NullPointerException。

下面的程序说明了comparingDouble(java.util.function.ToDoubleFunction)方法：
程序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 + "]";
    }
}

打印在IDE控制台的输出如下。

输出：

Java中的比较器comparingDouble方法及示例

程序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;
    }
}