Lambda expression in Java?

问题:

I need to switch part of my projects from C# to Java. But before which, I would like to compare two languages carefully and completely.

Regarding to lambda expression, I could write very elegant code via C#, the question is how to implement the same feature gracefully in Java? Thanks in advance!

class Program
{
    enum Gender
    {
        Male,
        Female
    }
    class Student
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public int Age { get; set; }
        public Gender Gender { get; set; }
        public override string ToString()
        {
            return string.Format("Id: {0}, Name: {1}, Age: {2}, Gender: {3}", Id, Name, Age, Gender);
        }
    }

    static void Main(string[] args)
    {
        var students = new[] { 
            new Student { Id = 1, Name = "Nathanial Archibald", Age = 18, Gender = Gender.Male },
            new Student { Id = 2, Name = "Georgina Sparks", Age = 19, Gender = Gender.Female },
            new Student { Id = 3, Name = "Daniel Humphrey", Age = 20, Gender = Gender.Male },
            new Student { Id = 4, Name = "Jenny Humphrey", Age = 17, Gender = Gender.Female },
        };

        var men = students.Where(p => p.Gender == Gender.Male);
        var ageAbove18 = students.Where(p => p.Age > 18);
        var humphrey = students.Where(p => p.Name.EndsWith("Humphrey"));
        var idGT1orderbyAge = students.Where(p => p.Id > 1).OrderBy(p => p.Age);

        foreach (var s in men) Console.WriteLine(s.ToString());
        foreach (var s in ageAbove18) Console.WriteLine(s.ToString());
        foreach (var s in humphrey) Console.WriteLine(s.ToString());
        foreach (var s in idGT1orderbyAge) Console.WriteLine(s.ToString());
    }
}

回答1:

Java in version 8 might support lambda.;)

You can use this Site or this. See this example:

final Array<Integer> a = array(1, 2, 3);  
final Array<Integer> b = a.map({int i => i + 42});  
arrayShow(intShow).println(b); // {43,44,45}  

回答2:

Currently java doesn't support Lambda operation, but this will going to be introduced in Java 8. For further reference site

But as you want to switch to Java this is a good option but as long as lambda operation is not supported you can create your methods to do the same task and after java 8 release shift to the lambha operation

here is an example of lambha operation in java 8

回答3:

Java 8 supports Lambda expression. Here is how you can use lambda expression in java to sort a list of Students

private static void sort(List<Student> students) {
Comparator<Student> rollNumberComparator = (student1, student2) -> 
    student1.getRollNumber().compareTo(student2.getRollNumber());

Collections.sort(students,rollNumberComparator);

}

You can refer : http://www.groupkt.com/post/088a8dea/lambda-expressions---java-8-feature.htm

回答4:

Lambda expressions aren't part of the current version of Java (1.7) it is a feature for Java 8, which wont be released at least until next year