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Wednesday, December 2, 2020

Lambda Expressions Examples Before And AfterJava 8

1. Introduction


In this tutorial, We'll learn how to write programs using java 8 lambda and Stream concepts with examples. Many developers feel learning java 8 concepts may be hard to understand. But once we are good using them then feel reduces error prone code and improves the performance of the application.

Read article on Java 8 Lamda Expression Rules

Examples Programs Before and After Java 8

In this article, We will see the example programs on sorting using Comparator, File names validation, Retrieving only hidden files and filtering list objects based on conditions.

2. Sorting - Lambda Expression

2.1 Before Java 8


See the below code which is implemented in older versions of Java. Here trying to sort the Employee's based on the id column.

Collections.sort(emplyeesList, new Comparator() {
 public int compare(Employee a1, Employee a2){
  return a1.getId().compareTo(a2.getId());
 }
});


Here, written code in 5 lines in which includes Comparator implementation.

2.2 In Java 8

See the below code in Java 8. All the code is in single line and not seeing comparing logic.

emplyeesList.sort(Comparator.comparing(Employee::getId));

Here, Comparator is a Functional Interface which has only one abstract method.

Comparator has a static method comparing(.Function.) which accepts only Funtion interface.
https://docs.oracle.com/javase/8/docs/api/java/util/function/Function.html

Note: Function<T, R> also a Functional Interface. This has a method apply(T t) which will be called from Comparator.comparing() method.

3. File Name Validation with Lambda Expression

3.1 Before Java 8


See the code in java old version. Here the core logic is file.getName().endsWith(".xml"); The remaining code is just syntax.

File[] hiddenFiles = new File("directory_name").listFiles(new FileFilter() {
 public boolean accept(File file) {
  return file.getName().endsWith(".xml");
 }
});

3.2 In Java 8

The above code is simplified to single line which reduces the errors.

File[] hiddenFiles = new File("directory_name").listFiles( file -> file.getName().endsWith(".xml"));

Note: Java 8, just focus on the business logic and takes its syntax internally. Developer need not to worry about it.


4. Retrieving only Hidden files - Lambda Expression

4.1 Before java 8


File has a method to check the method is hidden or not using isHidden() method.

File[] hiddenFiles = new File("directory_name").listFiles(new FileFilter() {
 public boolean accept(File file) {
  return file.isHidden();
 }
});

4.2 In Java 8

Just using the new Method Reference concept as part of new Java 8.

File[] hiddenFiles = new File("directory_name").listFiles(File::isHidden);


5. Conclusion


In this post, We've seen example lambda program before and after Java 8.

Observed the differences between them. Java 8 were in many ways more profound than any other changes to Java in its history.

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