Compile-time Builder Pattern in Java

Builder pattern is a pattern that is usually used for a language that does not support named parameters. However, the typical builder pattern has a limitation, such at it can't at compile-time check the required parameters. Below are some suggestions how to use a builder pattern that has compile-time check.

• Option 1

public class Foo {
    private String a;
    private String b;
    private String c;

    private Foo() {
    }

    public static ABuilder newBuilder() {
        return new ABuilder(new Foo());
    }

    private static class ABuilder {
        private final Foo foo;

        private ABuilder(Foo foo) {
            this.foo = foo;
        }

        public BBuilder a(String a) {
            foo.a = a;
            return new BBuilder(foo);
        }
    }

    private static class BBuilder {
        private final Foo foo;

        private BBuilder(Foo foo) {
            this.foo = foo;
        }

        public CBuilder b(String b) {
            foo.b = b;
            return new CBuilder(foo);
        }
    }

    private static class CBuilder {
        private final Foo foo;

        private CBuilder(Foo foo) {
            this.foo = foo;
        }

        public FinalBuilder c(String c) {
            foo.c = c;
            return new FinalBuilder(foo);
        }
    }

    private static class FinalBuilder {
        private final Foo foo;

        private FinalBuilder(Foo foo) {
            this.foo = foo;
        }

        public Foo build() {
            return foo;
        }
    }

    public static void main(String[] args) {
        Foo foo = Foo.newBuilder().a("a").b("b").c("c").build();
        System.out.println(foo);
    }
}

• Option 2

public class Bar {
    private final String a;
    private final String b;
    private final String c;

    public static class False {}
    public static class True {}

    public static class Builder<Has1, Has2, Has3> {
        private String a;
        private String b;
        private String c;

        public static Builder<False, False, False> create() {
            return new Builder<>();
        }

        public Builder<True, Has2, Has3> a(String a) {
            this.a = a;
            return (Builder<True, Has2, Has3>) this;
        }

        public Builder<Has1, True, Has3> b(String b) {
            this.b = b;
            return (Builder<Has1, True, Has3>) this;
        }

        public Builder<Has1, Has2, True> c(String c) {
            this.c = c;
            return (Builder<Has1, Has2, True>) this;
        }
    }

    public Bar(Builder<True, True, True> builder) {
        a = builder.a;
        b = builder.b;
        c = builder.c;
    }

    public static void main(String[] args) {
        Bar bar = new Bar(Builder.create().a("a").b("c").c("a"));
        System.out.println(bar);
    }
}