New in Java 16: record class

Previously, we used the class keyword to define classes, but starting from Java 16, we will add one more keyword record , which can also be used to define classes. The introduction of record keywords is mainly to provide a more concise and compact way of defining final classes.

Let's take a closer look at the details of the record class. Companion video tutorial: New in Java 16: Declaring classes with record

declare the record class

The basic syntax for declaring a record class:

 record range(int start, int end){}

We know that the class class can live in a separate file, or it can be declared in other classes. Then the record class is the same, it has the following declaration methods:

1. A separate document states:

 public record range(int start, int end){}

2. Declare inside the class:

 public class DidispaceTest {
    public record range(int start, int end){}
}

3. Declaration inside the function:

 public class DidispaceTest {
  public void test() {
    public record range(int start, int end){}
  }
}

Detailed explanation of record class

After knowing how to declare it, you will definitely want to use record to declare only a few elements, what capabilities will it have?

Because record keyword declaration class is mainly to simplify the declaration of some classes, so it is essentially a special class, or the class of a certain template.

record The declared class has these characteristics:

1. It is a final class
2. Automatically implement equals , hashCode , toString functions
3. Member variables are all public attributes

So, for the range class written earlier, it is equivalent to a class like this:

 public final class range{
    final int start;
    final int end;

    public range(int start, int end) {
        this.start = start;
        this.end = end;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        range range = (range) o;
        return start == range.start && end == range.end;
    }

    @Override
    public int hashCode() {
        return Objects.hash(start, end);
    }

    @Override
    public String toString() {
        return "range{" +
                "start=" + x +
                ", end=" + y +
                '}';
    }

    public int start(){
        return start;
    }

    public int end(){
        return end;
    }
}

Because some functions are hidden, we can't see them when the range is defined, so we can try to write a test code like this to verify:

 @Test
public void test() {
  range r = new range(100, 200);
  log.info(r.toString());

  range r2 = new range(100, 200);
  log.info(String.valueOf(r.equals(r2)));
}

define member function

Because record the essence of the declaration is also a class, so it is definitely possible to define member functions.

For example, we can define member functions in the record class like this:

 record range(int start, int end){
  int distance(){
    return end - start;
  }
}

Then, you can call it like this:

 range r = new range(100, 200);
r.distance();

If you encounter difficulties in the learning process? You can join our high-quality technical exchange group , participate in exchanges and discussions, and learn and progress better! Also, don't go away, follow me, and keep updating the new Java feature column !

Welcome to my public account: Programmer DD. Learn about cutting-edge industry news for the first time, share in-depth technical dry goods, and obtain high-quality learning resources