Not able to get defined variable value in function

I have below code.

public class TestClass {

  @Value("${api.key}")
  private String apiKey;

  @Value("${api.version}")
  private String apiVersion;

  private String baseURL = apiKey + "/" + apiVersion;

  public test() {
     LOGGER.debug("Val {}", baseURL);
  }
}  

When I try to run it always give null as a result.

I have same baseURL and in Once class I have multiple functions, so if any changes come no need to change in every function.

Static values are initialised before the beans creation, which means the values to the member fields will be injected after the static variable is assigned with values and thats the reason it's coming null.

What can be done is, you can use Spring's @PostConstruct above an init function and perform your operation there and assign the base url to the member variable, which can be accessed later.
Post Construct makes sure your code inside function is executed(only once) after your bean gets created.

    
public class TestClass {

  @Value("${api.key}")
  private String apiKey;

  @Value("${api.version}")
  private String apiVersion;

  private final String baseURL;

  @PostConstruct
  private init() {
    baseURL = apiKey + "/" + apiVersion;
  }

  public String getBaseUrl() {
    return baseUrl;
  }

  public test() {
     LOGGER.debug("Val {}", baseURL);
  }
}  

This is because static members will be initialized before the value of configKey will be injected. You can access configKey only if your TestClass is fully initialized. You can try something like this:

import lombok.extern.log4j.Log4j;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

import javax.annotation.PostConstruct;

@Log4j
@Component
public class TestClass {

    @Value("${config.key}")
    private String configKey;

    @PostConstruct
    void initialized() {
        this.test();
    }

    public void test() {
        log.debug(String.format("configKey: '%s'", this.configKey));
    }
}

And you should insert the following line into your application.properties:

config.key=something