Chained interface builder with inheritance

Cib.java

package com.phyous.cib;

public class Cain {

    public static void main(String[] args) {
        B b = new B.Builder().
            parent(
                new A.Builder()
                    .m1(1)
                    .m2(2)
                    .o1(3)
                    .o2(4)
            )
            .m3(5)
            .o3(6)
            .build();
        System.out.println(b.toString());

        C c = 
            new C.Builder().parent(new B.Builder().
                parent(
                    new A.Builder()
                        .m1(1)
                        .m2(2)
                        .o1(3)
                        .o2(4)
                )
                .m3(5)
                .o3(6))
            .m4(7)
            .o4(8)
            .build();
        System.out.println(c.toString());
 
    }

    static class A {
        int m1;
        int m2;

        int o1;
        int o2;

        @Override
        public String toString() {
            return String.format("m1: %d m2: %d o1: %d o2: %d", m1, m2, o1, o2);
        }

        static class Builder implements BuildM1, BuildM2 {
            int m1;
            int m2;
            int o1;
            int o2;

            // Used for concrete classes
            A build() {
                A a = new A();
                this.enhance(a);
                return a;
            }
            
            <T extends A> void enhance(T input) {
                input.m1 = this.m1;
                input.m2 = this.m2;
                input.o1 = this.o1;
                input.o2 = this.o2;
            }

            @Override
            public BuildM2 m1(int m1) {
                this.m1 = m1;
                return this;
            }

            @Override
            public Builder m2(int m2) {
                this.m2 = m2;
                return this;
            }

            public Builder o1(int o1) {
                this.o1 = o1;
                return this;
            }

            public Builder o2(int o2) {
                this.o2 = o2;
                return this;
            }
        }

        interface BuildM1 {
            BuildM2 m1(int m1);
        }

        interface BuildM2 {
            Builder m2(int m2);
        }


    }

    static class B extends A {
        int m3;
        int o3;
        
        @Override
        public String toString() {
            return super.toString() + String.format(" m3: %d o3: %d", m3, o3);
        }
        

        static class Builder extends A.Builder implements BuildParent, BuildM3 {
            int m3;
            int o3;
            A.Builder parentBuilder;

            @Override
            public Builder m3(int m3) {
                this.m3 = m3;
                return this;
            }

            public Builder o3(int o3) {
                this.o3 = o3;
                return this;
            }

            @Override
            public BuildM3 parent(A.Builder a) {
                parentBuilder = a;
                return this;
            }
            
            public B build() {
                B b = new B();
                this.enhance(b);
                return b;
            }

            <T extends B> void enhance(T input) {
                parentBuilder.enhance(input);
                input.m3 = m3;
                input.o3 = o3;
            }
        }

        interface BuildParent {
            BuildM3 parent(A.Builder a);
        }

        interface BuildM3 {
            Builder m3(int m3);
        }

    }

    static class C extends B {
        int m4;
        int o4;

        @Override
        public String toString() {
            return super.toString() + String.format(" m4: %d o4: %d", m4, o4);
        }


        static class Builder extends B.Builder implements BuildParent, BuildM4 {
            int m4;
            int o4;
            B.Builder parentBuilder;

            @Override
            public Builder m4(int m4) {
                this.m4 = m4;
                return this;
            }

            public Builder o4(int o4) {
                this.o4 = o4;
                return this;
            }

            @Override
            public BuildM4 parent(B.Builder b) {
                parentBuilder = b;
                return this;
            }

            public C build() {
                C c = new C();
                this.enhance(c);
                return c;
            }

            <T extends C> void enhance(T input) {
                parentBuilder.enhance(input);
                input.m4 = m4;
                input.o4 = o4;
            }
        }

        interface BuildParent {
            BuildM4 parent(B.Builder a);
        }

        interface BuildM4 {
            Builder m4(int m4);
        }

    } 
}