import java.io.*;
import java.util.*;

public class Props {
	
	private Properties props = new Properties();
	private static Props sysProps;
	
	public Props(String filename) {
		try {
			InputStream input = getClass().getResourceAsStream(filename);
			props.load(input);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
	
	public String getValue(String key) {
		if (key.equals("default")) {
			//return when value is null.
			return props.getProperty(key, "default");
		}
		return props.getProperty(key);
	}
	
	public String getValueAndPrint(String key) {
		String value = getValue(key);
		System.out.println(key + ":" + value);
		return value;
	}
	
	public void list() {
		props.list(System.out);
	}
	
	public static String getSysValue(String key) {
		if (sysProps == null) {
			sysProps = new Props("config.properties");
		}
		return sysProps.getValue(key);
	}
	
	public static void main(String[] args) {
		Props props = new Props("config.properties");
		props.list();
		props.getValueAndPrint("null");
		props.getValueAndPrint("name");
		props.getValueAndPrint("age");
		props.getValueAndPrint("novalue");
		
		System.out.println(getSysValue("null"));
		System.out.println(getSysValue("name"));
		System.out.println(getSysValue("age"));
		System.out.println(getSysValue("novalue"));
	}
}