Mixing
Java: Generic method for Enums
23
Help me understand generics. Say I have two enums as inner classes like so:
public class FoodConstants{
public static enum Vegetable {
POTATO,BROCCOLI,SQUASH,CARROT;
}
public static enum Fruit {
APPLE,MANGO,BANANA,GUAVA;
}
}
Instead of having both enums implement an interface, and have to implement the same method twice, I would like to have a method in the outer class that does something like:
public <e> String getEnumString<Enum<?> e, String s){
for(Enum en: e.values()){
if(en.name().equalsIgnoreCase(s)){
return s;
}
}
return null;
}
However this method does not compile. What I am trying to do is find out if a string value is the name of an enumerated value, in ANY enum, whether it's Vegetable, Fruit, what not.
Regardless of whether this is in fact a redundant method, what is wrong with the one I am trying to (re)write?
Basically I would like to do this:
public class FoodConstants{
public static enum Vegetable {
POTATO,BROCCOLI,SQUASH,CARROT;
}
public static enum Fruit {
APPLE,MANGO,BANANA,GUAVA;
}
public <e> String getEnumString<Enum<?> e, String s){
for(Enum en: e.values()){
if(en.name().equalsIgnoreCase(s)){
return s;
}
}
return null;
}
} //end of code
java generics enums
edited Jun 21 '18 at 8:15
halfer
14.7k759116
asked May 6 '13 at 20:00
Alexander MillsAlexander Mills
20.2k35163351
add a comment |
23
Help me understand generics. Say I have two enums as inner classes like so:
public class FoodConstants{
public static enum Vegetable {
POTATO,BROCCOLI,SQUASH,CARROT;
}
public static enum Fruit {
APPLE,MANGO,BANANA,GUAVA;
}
}
Instead of having both enums implement an interface, and have to implement the same method twice, I would like to have a method in the outer class that does something like:
public <e> String getEnumString<Enum<?> e, String s){
for(Enum en: e.values()){
if(en.name().equalsIgnoreCase(s)){
return s;
}
}
return null;
}
However this method does not compile. What I am trying to do is find out if a string value is the name of an enumerated value, in ANY enum, whether it's Vegetable, Fruit, what not.
Regardless of whether this is in fact a redundant method, what is wrong with the one I am trying to (re)write?
Basically I would like to do this:
public class FoodConstants{
public static enum Vegetable {
POTATO,BROCCOLI,SQUASH,CARROT;
}
public static enum Fruit {
APPLE,MANGO,BANANA,GUAVA;
}
public <e> String getEnumString<Enum<?> e, String s){
for(Enum en: e.values()){
if(en.name().equalsIgnoreCase(s)){
return s;
}
}
return null;
}
} //end of code
java generics enums
edited Jun 21 '18 at 8:15
halfer
14.7k759116
asked May 6 '13 at 20:00
Alexander MillsAlexander Mills
20.2k35163351
add a comment |
23
23
23
4
Help me understand generics. Say I have two enums as inner classes like so:
public class FoodConstants{
public static enum Vegetable {
POTATO,BROCCOLI,SQUASH,CARROT;
}
public static enum Fruit {
APPLE,MANGO,BANANA,GUAVA;
}
}
Instead of having both enums implement an interface, and have to implement the same method twice, I would like to have a method in the outer class that does something like:
public <e> String getEnumString<Enum<?> e, String s){
for(Enum en: e.values()){
if(en.name().equalsIgnoreCase(s)){
return s;
}
}
return null;
}
However this method does not compile. What I am trying to do is find out if a string value is the name of an enumerated value, in ANY enum, whether it's Vegetable, Fruit, what not.
Regardless of whether this is in fact a redundant method, what is wrong with the one I am trying to (re)write?
Basically I would like to do this:
public class FoodConstants{
public static enum Vegetable {
POTATO,BROCCOLI,SQUASH,CARROT;
}
public static enum Fruit {
APPLE,MANGO,BANANA,GUAVA;
}
public <e> String getEnumString<Enum<?> e, String s){
for(Enum en: e.values()){
if(en.name().equalsIgnoreCase(s)){
return s;
}
}
return null;
}
} //end of code
java generics enums
edited Jun 21 '18 at 8:15
halfer
14.7k759116
asked May 6 '13 at 20:00
Alexander MillsAlexander Mills
20.2k35163351
Help me understand generics. Say I have two enums as inner classes like so:
public class FoodConstants{
public static enum Vegetable {
POTATO,BROCCOLI,SQUASH,CARROT;
}
public static enum Fruit {
APPLE,MANGO,BANANA,GUAVA;
}
}
Instead of having both enums implement an interface, and have to implement the same method twice, I would like to have a method in the outer class that does something like:
public <e> String getEnumString<Enum<?> e, String s){
for(Enum en: e.values()){
if(en.name().equalsIgnoreCase(s)){
return s;
}
}
return null;
}
However this method does not compile. What I am trying to do is find out if a string value is the name of an enumerated value, in ANY enum, whether it's Vegetable, Fruit, what not.
Regardless of whether this is in fact a redundant method, what is wrong with the one I am trying to (re)write?
Basically I would like to do this:
public class FoodConstants{
public static enum Vegetable {
POTATO,BROCCOLI,SQUASH,CARROT;
}
public static enum Fruit {
APPLE,MANGO,BANANA,GUAVA;
}
public <e> String getEnumString<Enum<?> e, String s){
for(Enum en: e.values()){
if(en.name().equalsIgnoreCase(s)){
return s;
}
}
return null;
}
} //end of code
java generics enums
java generics enums
edited Jun 21 '18 at 8:15
halfer
14.7k759116
asked May 6 '13 at 20:00
Alexander MillsAlexander Mills
20.2k35163351
edited Jun 21 '18 at 8:15
halfer
14.7k759116
asked May 6 '13 at 20:00
Alexander MillsAlexander Mills
20.2k35163351
edited Jun 21 '18 at 8:15
halfer
14.7k759116
edited Jun 21 '18 at 8:15
halfer
14.7k759116
edited Jun 21 '18 at 8:15
halfer
14.7k759116
14.7k759116
asked May 6 '13 at 20:00
Alexander MillsAlexander Mills
20.2k35163351
asked May 6 '13 at 20:00
Alexander MillsAlexander Mills
20.2k35163351
asked May 6 '13 at 20:00
Alexander MillsAlexander Mills
20.2k35163351
20.2k35163351
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
52
public static <E extends Enum<E>>
String getEnumString(Class<E> clazz, String s){
for(E en : EnumSet.allOf(clazz)){
if(en.name().equalsIgnoreCase(s)){
return en.name();
}
}
return null;
}
The original has a few problems:
- It accepts an instance of the enum instead of the class representing the enum
which your question suggests you want to use. - The type parameter isn't used.
- It returns the input instead of the instance name. Maybe returning the instance would be more useful -- a case-insensitive version of
Enum.valueOf(String). - It calls a static method on an instance so you can iterate.
EnumSetdoes all the reflective stuff for you.
answered May 6 '13 at 20:06
Mike SamuelMike Samuel
94.4k23174215
6
Oh, and clazz.getEnumConstants() would work instead of EnumSet.allOf(clazz). It's probably slightly more efficient, given that EnumSet.allOf is probably implemented in terms of it, but then, maybe not.
– Sebastian Redl
May 6 '13 at 20:12
@SebastianRedl, Odd. I thought that wasn't available in 1.5 but apparently it is.
– Mike Samuel
May 6 '13 at 20:13
6
@SebastianRedl: actually,EnumSet.allOf()is more efficient than.getEnumConstants(), because.getEnumConstants()must make a copy of the internal array of constants (since it returns an array, and there is no way to prevent an array from being modified), whereasEnumSetcan use internal implementation details to directly iterate over the internal array.
– newacct
May 7 '13 at 5:54
using this signature it causes for me a "bad class file", "undeclared type variable: T" errors on compile
– Joe Cabezas
Apr 22 '16 at 22:40
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
52
public static <E extends Enum<E>>
String getEnumString(Class<E> clazz, String s){
for(E en : EnumSet.allOf(clazz)){
if(en.name().equalsIgnoreCase(s)){
return en.name();
}
}
return null;
}
The original has a few problems:
- It accepts an instance of the enum instead of the class representing the enum
which your question suggests you want to use. - The type parameter isn't used.
- It returns the input instead of the instance name. Maybe returning the instance would be more useful -- a case-insensitive version of
Enum.valueOf(String). - It calls a static method on an instance so you can iterate.
EnumSetdoes all the reflective stuff for you.
answered May 6 '13 at 20:06
Mike SamuelMike Samuel
94.4k23174215
6
Oh, and clazz.getEnumConstants() would work instead of EnumSet.allOf(clazz). It's probably slightly more efficient, given that EnumSet.allOf is probably implemented in terms of it, but then, maybe not.
– Sebastian Redl
May 6 '13 at 20:12
@SebastianRedl, Odd. I thought that wasn't available in 1.5 but apparently it is.
– Mike Samuel
May 6 '13 at 20:13
6
@SebastianRedl: actually,EnumSet.allOf()is more efficient than.getEnumConstants(), because.getEnumConstants()must make a copy of the internal array of constants (since it returns an array, and there is no way to prevent an array from being modified), whereasEnumSetcan use internal implementation details to directly iterate over the internal array.
– newacct
May 7 '13 at 5:54
using this signature it causes for me a "bad class file", "undeclared type variable: T" errors on compile
– Joe Cabezas
Apr 22 '16 at 22:40
add a comment |
52
public static <E extends Enum<E>>
String getEnumString(Class<E> clazz, String s){
for(E en : EnumSet.allOf(clazz)){
if(en.name().equalsIgnoreCase(s)){
return en.name();
}
}
return null;
}
The original has a few problems:
- It accepts an instance of the enum instead of the class representing the enum
which your question suggests you want to use. - The type parameter isn't used.
- It returns the input instead of the instance name. Maybe returning the instance would be more useful -- a case-insensitive version of
Enum.valueOf(String). - It calls a static method on an instance so you can iterate.
EnumSetdoes all the reflective stuff for you.
answered May 6 '13 at 20:06
Mike SamuelMike Samuel
94.4k23174215
6
Oh, and clazz.getEnumConstants() would work instead of EnumSet.allOf(clazz). It's probably slightly more efficient, given that EnumSet.allOf is probably implemented in terms of it, but then, maybe not.
– Sebastian Redl
May 6 '13 at 20:12
@SebastianRedl, Odd. I thought that wasn't available in 1.5 but apparently it is.
– Mike Samuel
May 6 '13 at 20:13
6
@SebastianRedl: actually,EnumSet.allOf()is more efficient than.getEnumConstants(), because.getEnumConstants()must make a copy of the internal array of constants (since it returns an array, and there is no way to prevent an array from being modified), whereasEnumSetcan use internal implementation details to directly iterate over the internal array.
– newacct
May 7 '13 at 5:54
using this signature it causes for me a "bad class file", "undeclared type variable: T" errors on compile
– Joe Cabezas
Apr 22 '16 at 22:40
add a comment |
52
52
52
public static <E extends Enum<E>>
String getEnumString(Class<E> clazz, String s){
for(E en : EnumSet.allOf(clazz)){
if(en.name().equalsIgnoreCase(s)){
return en.name();
}
}
return null;
}
The original has a few problems:
- It accepts an instance of the enum instead of the class representing the enum
which your question suggests you want to use. - The type parameter isn't used.
- It returns the input instead of the instance name. Maybe returning the instance would be more useful -- a case-insensitive version of
Enum.valueOf(String). - It calls a static method on an instance so you can iterate.
EnumSetdoes all the reflective stuff for you.
answered May 6 '13 at 20:06
Mike SamuelMike Samuel
94.4k23174215
public static <E extends Enum<E>>
String getEnumString(Class<E> clazz, String s){
for(E en : EnumSet.allOf(clazz)){
if(en.name().equalsIgnoreCase(s)){
return en.name();
}
}
return null;
}
The original has a few problems:
- It accepts an instance of the enum instead of the class representing the enum
which your question suggests you want to use. - The type parameter isn't used.
- It returns the input instead of the instance name. Maybe returning the instance would be more useful -- a case-insensitive version of
Enum.valueOf(String). - It calls a static method on an instance so you can iterate.
EnumSetdoes all the reflective stuff for you.
answered May 6 '13 at 20:06
Mike SamuelMike Samuel
94.4k23174215
edited Apr 17 '14 at 15:34
answered May 6 '13 at 20:06
Mike SamuelMike Samuel
94.4k23174215
answered May 6 '13 at 20:06
Mike SamuelMike Samuel
94.4k23174215
answered May 6 '13 at 20:06
Mike SamuelMike Samuel
94.4k23174215
94.4k23174215
6
Oh, and clazz.getEnumConstants() would work instead of EnumSet.allOf(clazz). It's probably slightly more efficient, given that EnumSet.allOf is probably implemented in terms of it, but then, maybe not.
– Sebastian Redl
May 6 '13 at 20:12
@SebastianRedl, Odd. I thought that wasn't available in 1.5 but apparently it is.
– Mike Samuel
May 6 '13 at 20:13
6
@SebastianRedl: actually,EnumSet.allOf()is more efficient than.getEnumConstants(), because.getEnumConstants()must make a copy of the internal array of constants (since it returns an array, and there is no way to prevent an array from being modified), whereasEnumSetcan use internal implementation details to directly iterate over the internal array.
– newacct
May 7 '13 at 5:54
using this signature it causes for me a "bad class file", "undeclared type variable: T" errors on compile
– Joe Cabezas
Apr 22 '16 at 22:40
add a comment |
6
Oh, and clazz.getEnumConstants() would work instead of EnumSet.allOf(clazz). It's probably slightly more efficient, given that EnumSet.allOf is probably implemented in terms of it, but then, maybe not.
– Sebastian Redl
May 6 '13 at 20:12
@SebastianRedl, Odd. I thought that wasn't available in 1.5 but apparently it is.
– Mike Samuel
May 6 '13 at 20:13
6
@SebastianRedl: actually,EnumSet.allOf()is more efficient than.getEnumConstants(), because.getEnumConstants()must make a copy of the internal array of constants (since it returns an array, and there is no way to prevent an array from being modified), whereasEnumSetcan use internal implementation details to directly iterate over the internal array.
– newacct
May 7 '13 at 5:54
using this signature it causes for me a "bad class file", "undeclared type variable: T" errors on compile
– Joe Cabezas
Apr 22 '16 at 22:40
6
6
Oh, and clazz.getEnumConstants() would work instead of EnumSet.allOf(clazz). It's probably slightly more efficient, given that EnumSet.allOf is probably implemented in terms of it, but then, maybe not.
– Sebastian Redl
May 6 '13 at 20:12
Oh, and clazz.getEnumConstants() would work instead of EnumSet.allOf(clazz). It's probably slightly more efficient, given that EnumSet.allOf is probably implemented in terms of it, but then, maybe not.
– Sebastian Redl
May 6 '13 at 20:12
@SebastianRedl, Odd. I thought that wasn't available in 1.5 but apparently it is.
– Mike Samuel
May 6 '13 at 20:13
@SebastianRedl, Odd. I thought that wasn't available in 1.5 but apparently it is.
– Mike Samuel
May 6 '13 at 20:13
6
6
@SebastianRedl: actually,
EnumSet.allOf() is more efficient than .getEnumConstants(), because .getEnumConstants() must make a copy of the internal array of constants (since it returns an array, and there is no way to prevent an array from being modified), whereas EnumSet can use internal implementation details to directly iterate over the internal array.– newacct
May 7 '13 at 5:54
@SebastianRedl: actually,
EnumSet.allOf() is more efficient than .getEnumConstants(), because .getEnumConstants() must make a copy of the internal array of constants (since it returns an array, and there is no way to prevent an array from being modified), whereas EnumSet can use internal implementation details to directly iterate over the internal array.– newacct
May 7 '13 at 5:54
using this signature it causes for me a "bad class file", "undeclared type variable: T" errors on compile
– Joe Cabezas
Apr 22 '16 at 22:40
using this signature it causes for me a "bad class file", "undeclared type variable: T" errors on compile
– Joe Cabezas
Apr 22 '16 at 22:40
add a comment |
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