I am currently trying to learn streams in Java, however I stumbled upon a problem I couldn't solve on my own. Given a List of Person objects with the attributes age, height and name. I want to write a ,java,java-8,java-stream"/>

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I am currently trying to learn streams in Java, however I stumbled upon a problem I couldn't solve on my own. Given a List of Person objects with the attributes age, height and name. I want to write a

java - List的Java流排序元素

I am currently trying to learn streams in Java, however I stumbled upon a problem I couldn't solve on my own. Given a List of Person objects with the attributes age, height and name. I want to write a

问题描述

I am currently trying to learn streams in Java, however I stumbled upon a problem I couldn't solve on my own. Given a List of Person objects with the attributes age, height and name. I want to write a method toString(), that sorts the List by height and in case the heights are equal by age (everything in descending order). Is there a possibility to solve this with a stream? I know how to sort the List by height, however I don't understand how you would get the equal elements (Persons with the same height) and sort them as well by age.

Class Person:

public class Person {
    private int age;
    private double height;
    private String name;

    public Person(int age, double height, String name){
        this.age = age;
        this.height = height;
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public double getHeight() {
        return height;
    }

    public String getName() {
        return name;
    }
}

The Data class (where you create the toString method):

public class Data {
    private List<Person> persons;

    public Data(List<Person> persons){
        this.persons = persons;
    }

    public String toString(){
        //sort the list (persons) and return a String of names

        return "";
    }
}

gnuplot: how to convert 12h time format into 24h time format?

How can I convert the annoying 12h time format (with AM and PM) into the 24h time format?

I wanted to avoid external programs like awk as in this example.

Since gnuplot has a time-specifier %p for "am" and "pm" (check help time_specifiers), I thought it would be easy. But the following code does not give the correct result, but a warning message:

warning: Bad time format in string

Maybe, I'm using %p incorrectly?

Code:

### change 12h time format to 24h format (does not give correct results)
reset session

$Data12 <<EOD
12/31/19  8:12:01 AM
12/31/19  8:12:02 PM
12/31/19 12:00:03 am
12/31/19 12:00:04 pm
EOD

myTimeFmt12 = "%m/%d/%y %H:%M:%S %p"
myTimeFmt24 = "%d.%m.%Y %H:%M:%S"

set table $Data24
    plot $Data12 u (strftime(myTimeFmt24,timecolumn(1,myTimeFmt12))) w table
unset table
print $Data24
### end of code

Result:

         "tbTime12to24.plt" line 15: warning: Bad time format in string
         "tbTime12to24.plt" line 15: warning: Bad time format in string
         "tbTime12to24.plt" line 15: warning: Bad time format in string
         "tbTime12to24.plt" line 15: warning: Bad time format in string
 31.12.2019 08:12:01    
 31.12.2019 08:12:02    
 31.12.2019 12:00:03    
 31.12.2019 12:00:04

标签： javajava-8java-stream

解决方案

您可以使用比较器链接按高度排序，然后按年龄排序。然后使用map运算符映射名称，最后加入收集器以将名称连接成您感兴趣的格式化字符串。这是它的外观。

String sortedNames = persons.stream()
    .sorted(Comparator.comparingDouble(Person::getHeight)
        .thenComparingDouble(Person::getAge).reversed())
    .map(Person::getName)
    .collect(Collectors.joining(", "));

PS 但是，我不认为double是代表一个人年龄的好数据类型。int 将是一个更好的替代 IMO。

更新：

如果您有int数据类型来表示一个人的年龄，那么比较器链应该如下所示。其他一切都保持不变。

Comparator.comparingDouble(Person::getHeight)
        .thenComparingInt(Person::getAge).reversed()

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