d_correct.java

interface IProgram {
	public void work();
}

class Program implements IProgram{
	public void work() {
		// ....code
	}
}

class SuperProgram implements IProgram{
	public void work() {
		//....code
	}
}

class Engineer{
	IProgram program;

	public void setProgram(IProgram p) {
		program = p;
	}

	public void manage() {
		program.work();
	}
}