public class ClassToBuild {
	
	private final String someString;

	public ClassToBuild(String someString) {
		this.someString = someString;
	}
}

public class ClassToBuild {
	
	private final String someString;

	private ClassToBuild(String someString) {
		this.someString = someString;
	}
	
	public static final class Builder {
		
		private String someString;
		
		public Builder withSomeString(String someString) {
			this.someString = someString;
		}
		
		public ClassToBuild build() {
			return new ClassToBuild(someString);
		}
	}
}