Method Chaining Example

Example.java

package tld.examples;

public class Example {

    protected String mandatory;
    protected String optional;
    protected String mandatoryIfOptionalExists;

    private Example() {
    }

    public Example(final Example.Builder builder) {
        this.mandatory = builder.entity.mandatory;
        this.optional = builder.entity.optional;
        this.mandatoryIfOptionalExists = builder.entity.mandatoryIfOptionalExists;
    }

    public String getMandatory() {
        return this.mandatory;
    }

    public String getOptional() {
        return this.optional;
    }

    public String getMandatoryIfOptionalExists() {
        return this.mandatoryIfOptionalExists;
    }

    public static class Builder<T extends Example> {

        protected final T entity;

        public Builder() {
            this((T) new Example());
        }

        public Builder(final T abstractEntity) {
            this.entity = abstractEntity;
        }

        public Builder withMandatory(final String mandatory) {
            this.entity.mandatory = mandatory;
            return this;
        }

        public Builder withOptional(final String optional) {
            this.entity.optional = optional;
            return this;
        }

        public Builder withMandatoryIfOptionalExists(final String mandatoryIfOptionalExists) {
            this.entity.mandatoryIfOptionalExists = mandatoryIfOptionalExists;
            return this;
        }

        public Example build() {

            if (this.entity.optional != null
                    && !"".equals(this.entity.optional.trim())) {
                if (this.entity.mandatoryIfOptionalExists == null
                        || "".equals(this.entity.mandatoryIfOptionalExists.trim())) {
                    throw new IllegalArgumentException();
                }
            }

            return new Example(this);
        }

    }

}