比较器比较Java中的Double()方法和例子

Java 中 Comparator 接口的 comparisonDouble( Java Java.ToDoubleFunction )方法接受一个函数作为参数，该函数从类型 T 中提取双排序键，并返回一个按该排序键进行比较的 Comparator。返回的比较器是可序列化的，如果指定的函数也是可序列化的。

句法：

static  Comparator comparingDouble(
    ToDoubleFunction  keyExtractor)

参数：此方法接受单个参数keyExtractor ，它是用于提取双排序键的函数。

返回值：此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，此方法将抛出 NullPointerException。

下面的程序说明了 compareDouble(Java 函数.ToDoubleFunction) 方法：
方案一：

// 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 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 {
    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 控制台上的输出如下所示。
输出：

方案二：

// 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 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 {
    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： https: Java Java 函数)