If your enum class is required to have static fields, keep in mind they are created after the enum values themselves. That means, the following code will result in a NullPointerException:
enum Example {
ONE(1), TWO(2);
static Map<String, Integer> integers = new HashMap<>();
private Example(int value) {
integers.put(this.name(), value);
}
}A possible way to fix this:
enum Example {
ONE(1), TWO(2);
static Map<String, Integer> integers;
private Example(int value) {
putValue(this.name(), value);
}
private static void putValue(String name, int value) {
if (integers == null)
integers = new HashMap<>();
integers.put(name, value);
}
}Do not initialize the static field:
enum Example {
ONE(1), TWO(2);
// after initialisisation integers is null!!
static Map<String, Integer> integers = null;
private Example(int value) {
putValue(this.name(), value);
}
private static void putValue(String name, int value) {
if (integers == null)
integers = new HashMap<>();
integers.put(name, value);
}
// !!this may lead to null poiner exception!!
public int getValue(){
return (Example.integers.get(this.name()));
}
}initialisisation: