Java basic

OilProduct.java

public enum OilProduct {
 
    GASOLINE("휘발유", 1), HIGH_GRADE_GASOLINE("고급휘발유", 2), DIESEL("경유", 3);
 
    private String name;
    private int productId;
    private static Map<Integer, OilProduct> enumMap = new HashMap<Integer, OilProduct>();
 
    static {
        for (OilProduct each : OilProduct.values()) {
           enumMap.put(each.getProductId(), each);
        }
    }
 
     private OilProduct(String name, int productId) {
     this.name = name;
     this.productId = productId;
 }
 
    public String getName() {
        return name;
    }
 
    public int getProductId() {
        return productId;
    }
 
    public static OilProduct fromProductId(int id) {
        OilProduct matched = enumMap.get(id);
 
        if (matched == null) {
           throw newIllegalArgumentException("cannot find OilProduct for productId:" + id);
        }
 
        return matched;
    }
}