Lombok @builder annotation

@Builder Use of annotations

@Builder
public class Card {
    private int id;
    private String name;
    private boolean sex;
}

Card card = Card.builder().
            id(10).name("dasd").sex(true).
            build();

advantage

• It doesn't need too much set Method to define the property content
• More elegant writing

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@Builder What's done to the class ？

We can decompile the generated Card.class

public class Card {
    private int id;
    private String name;
    private boolean sex;

    Card(int id, String name, boolean sex) {
        this.id = id;
        this.name = name;
        this.sex = sex;
    }

    public static Card.CardBuilder builder() {
        return new Card.CardBuilder();
    }

    public static class CardBuilder {
        private int id;
        private String name;
        private boolean sex;

        CardBuilder() {
        }

        public Card.CardBuilder id(int id) {
            this.id = id;
            return this;
        }

        public Card.CardBuilder name(String name) {
            this.name = name;
            return this;
        }

        public Card.CardBuilder sex(boolean sex) {
            this.sex = sex;
            return this;
        }

        public Card build() {
            return new Card(this.id, this.name, this.sex);
        }

        public String toString() {
            return "Card.CardBuilder(id=" + this.id + ", name=" + this.name + ", sex=" + this.sex + ")";
        }
    }
}

Well, it's obvious , Annotations are compiled to make Card There is one more class named Card.CardBuilder The static inner class of . This static class has and Card Class has the same properties , And he implemented some extra methods ：

1.name、sex、id And so on

In fact, these methods and setAttribute Very similar , It's just the extra return of the instance itself , This makes it possible to write something like a chain call .

2.build Method

This method calls Card Class to generate Card example .

Card Class is still implemented builder Method , This method generates an empty Card.CardBuilder example

shortcoming

The most obvious point , It's generating Card Before instance , In fact, we created a Card.CardBuilder example , This obviously takes up extra memory .

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additional

@Builder(toBuilder = true)

This option allows you to instantiate a good Card, Update fields to generate new Card example .

public Card.CardBuilder toBuilder() {
    return (new Card.CardBuilder()).id(this.id).name(this.name).sex(this.sex);
}

 public static void main(String[] args) {
        Card card = Card.builder().id(10).name(" Mercedes ").sex(true).build();
        Card card1 = card.toBuilder().name(" BMW ").build();
        System.out.println(card);
        System.out.println(card1);
    }

Card(id=10, name= Mercedes , sex=true)
Card(id=10, name= BMW , sex=true)