[JAVA] I made a question that can be used for a technical interview

Target audience

I want to have a technical interview for an engineer educator, but I can't think of a good question.

Target position

--Tech lead to improve the productivity of the development team --Software development and education staff who are also in charge of programming education and code review


--An interface written without knowing the benefits of the interface will not bring that benefit ――The goodness is not reflected in the program written without understanding the key of the language specification.

Purpose of the question

Confirmation of whether the design can be designed with development efficiency and maintenance efficiency in mind, and whether the code can be discussed with engineers for design and code improvement.

Question 1

  1. What are the benefits of abstracting a class?
  2. Why should classes rely on abstraction rather than concreteness?
  3. Please explain the specifications of polymorphism and its purpose.

Question 2

  1. Please improve the following code by refactoring
  2. Please explain the points of improvement and their benefits.

Code (Java)


public interface InterfaceA {	
	String search(String key);
	String delete(String key);
	String insert(String key);

public class ServiceA implements InterfaceA {
	public String search(String key) {
		return null;

	public String delete(String key) {
		return null;

	public String insert(String key) {
		return null;


public class ServiceController {

	private static ServiceA objA;
	private static ServiceB objB;
	private static ServiceC objC;
	public static void set(ServiceA obj) {
		objA = obj;		
	public static void set(ServiceB obj) {
		objB = obj;		
	public static void set(ServiceC obj) {
		objC = obj;		
	public static void search(int serviceType, String key) throws Exception {
		if(1 == serviceType)	 objA.search(key);
		else if(2 == serviceType)objB.search(key);
		else if(3 == serviceType)objC.search(key);
		else throw new Exception("Error");


public class Provider {

	public static void init() {		
		ServiceController.set(new ServiceA());
		ServiceController.set(new ServiceB());
		ServiceController.set(new ServiceC());		

	public static void searchA(String key) throws Exception {
		ServiceController.search(1, key);


These are the questions for code reviewers and educators.

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