public class TableContent {
public static String EXCEL_SHEET_NAME = Nit.THEAD.getName();
public static String FILENAME= Nit.FILENAME.getName();
public enum Nit {
FILENAME("Nit-workorder-list"),
THEAD("NIT WORKORDER"),
TENDERSPECNO("TENDER SPECFICATION NO."),
FEE("TENDER FEE"),
SDAMOUNT("SD AMOUNT"),
TYPE("NIT TYPE"),
PRE_BID("PRE BIDDING DATE"),
OPEN_DATE("OPENING DATE"),
STATUS("CONTRACTOR STATUS");
private final String name;
public String getName() {
return name;
}
private Nit(String name) {
this.name = name;
}
public static Nit getNitHeadByName(String name)
{
Nit[] nit=Nit.values();
if(nit==null)
{
return null;
}
for(Nit nitHead:nit)
{
if(nitHead.getName().equals(name))
return nitHead;
}
return null;
}
public enum NitWorkOrder {
}
public enum NitList {
}
My objective is:
I want to export excel sheet from my application, every time I need to hardcode the table headings, which was not good programming practice.
So I use enum to overcome the hardcode problem. Now there are different table heading according to the list, then I enclosed all the required ENUMS in single class.
I used to write getXXXByName() and getXXXByValue() to access the enum, by name or by value.
But he problem is I need to write getXXXByName() and getXXXByValue() everytime inside each enum. I want to write these methods inside the class and outside the enums, and access those methods with the help of class name.
I just want to declare my constants inside enum.
Please kindly suggest me an idea or a way so I can make this method universal which will work for each and every enum. I want to write these methods in such a way so it can be accessed for all enums enclosed in my class. I thought about generics but I have little knowledge.
You can use generics to push functionality up to a parent class by telling the parent class that the type is an enum that implements an interface.
// Use an interface to inform the super class what the enums can do.
public interface Named {
public String getName();
}
// Super class of all Tables.
public static class Table<E extends Enum<E> & Named> {
private final Class<E> itsClass;
private final String sheetName;
private final String fileName;
public Table(Class<E> itsClass) {
this.itsClass = itsClass;
// Walk the enum to get filename and sheet name.
String sheetName = null;
String fileName = null;
for ( E e: itsClass.getEnumConstants() ){
if ( e.name().equals("FILENAME")) {
fileName = e.getName();
}
if ( e.name().equals("THEAD")) {
sheetName = e.getName();
}
}
this.sheetName = sheetName;
this.fileName = fileName;
}
// Use the interface and the enum details to do your stuff.
public E getByName (String name) {
for ( E e: itsClass.getEnumConstants() ){
if ( e.getName().equals(name)) {
return e;
}
}
return null;
}
}
// Extend Table and tell it about your enum using the super constructor.
public static class TableContent extends Table<TableContent.Nit> {
public TableContent() {
super(TableContent.Nit.class);
}
public enum Nit implements Named{
FILENAME("Nit-workorder-list"),
THEAD("NIT WORKORDER"),
TENDERSPECNO("TENDER SPECFICATION NO."),
FEE("TENDER FEE"),
SDAMOUNT("SD AMOUNT"),
TYPE("NIT TYPE"),
PRE_BID("PRE BIDDING DATE"),
OPEN_DATE("OPENING DATE"),
STATUS("CONTRACTOR STATUS");
private final String name;
Nit(String name) {
this.name = name;
}
public String getName() {
return name;
}
}
}
Related
I am in a situation, where I'm trying to implement a (relatively simple) abstract syntax tree. All of the nodes inherit from a type called SimpleNode containing some code to store line and column information and accepting a visitor.
Now, some of the nodes should also be nameable, while others should have a property "accessible" (eg. public or private). Some nodes should even support both interfaces.
I'd preferably implement this using virtual inheritance and write two classes NameableNode and AccessibleNode, but Java doesn't support MI.
Eg NameableNode might have field "name" and implement simple getters and setters for this field. Similarly, AccessibleNode might also have a field "accessibility" and getters/setters.
What is a good way to implement this and avoid introducing code duplication in a huge part of the code base?
Small code example:
public class SimpleNode {
private int line = 0;
private int column = 0;
/* Getters and setters for line/column. */
/* ... */
}
public class NameableNode extends SimpleNode {
private String name = "";
/* Getters and setters for name */
}
public class AccessibleNode extends SimpleNode {
private boolean isPublic = false;
/* Getters and setters for accessibility */
}
You're looking for composition. There are many flavors of this - I will propose one that, from my understanding of what you're trying to build, should suit your purpose.
First, let's create some interfaces for yours Nodes:
public interface Nameable {
/* Getters and setters for name */
}
public interface Accessible {
/* Getters and setters for accessibility */
}
Next, you probably don't want to repeat the same implementation for every Node, so let's create those implementations:
public class NameDelegate() {
private String name = "";
/* Getters and setters for name */
}
public class AccessDelegate() {
private boolean isPublic = false;
/* Getters and setters for accessibility */
}
Now, let's put everything together:
public class SomeNodeA extends SimpleNode implements Nameable {
private NameDelegate nameDelegate;
public SomeNodeA(NameDelegate nameDelegate) {
this.nameDelegate = nameDelegate;
}
#Override
public String getName() {
return nameDelegate.getName();
}
#Override
public String setName(String name) {
nameDelegate.setName(name);
}
}
You can also have both behaviours in a single class:
public class SomeNodeB extends SimpleNode implements Nameable, Accessible {
private NameDelegate nameDelegate;
private AccessDelegate accessDelegate;
public SomeNodeB(NameDelegate nameDelegate, AccessDelegate accessDelegate) {
this.nameDelegate = nameDelegate;
this.accessDelegate = accessDelegate;
}
#Override
public String getName() {
return nameDelegate.getName();
}
#Override
public String setName(String name) {
nameDelegate.setName(name);
}
#Override
public boolean getAccessibility() {
return accessDelegate.getAccessibility();
}
/* etc... */
}
The idea is, you can package the state and the functionality of the different "features" into individual delegates, and expose them as corresponding interfaces in your Nodes.
Also, when operating on the Nodes, if you need to know whether a given instance of a Node supports a specific feature, you can use instanceof - e.g.:
if (someNode instanceof Nameable) {
// do naming stuff
}
In this case I would use the composition approach over inheritance:
public class Node {
private int line = 0;
private int column = 0;
/* Getters and setters for line/column. */
/* ... */
private String name = null;
public String getName() {
return this.name;
}
public void setName(String name) {
this._name = name;
}
private Boolean _isPublic = null;
public String isPublic() {
return this.name;
}
public void setIsPublic(boolean isPublic) {
this._isPublic = isPublic;
}
public boolean hasAccessibility() {
return this._isPublic != null;
}
public boolean hasName() {
return this._name != null;
}
}
Another solution that I like a bit more is creating these attributes dynamically using a HashMap and an enum that indicates all the possible attributes of a node. This way is more generic, as it requires to write less code for supporting new attributes, But it is also less typesafe(ish), as the additional attributes need to be casted at runtime:
import java.util.HashMap;
enum NodeAttribute {
NAME,
ACCESSIBILTY
}
enum NodeAccessibility {
PUBLIC,
PRIVATE
}
public class Node {
private int line = 0;
private int column = 0;
// Notice that this Object usage might involve some boxing for attributes of premitive type
private HashMap<NodeAttribute, Object> additionalAttributes = new HashMap<NodeAttribute, Object>();
/* Getters and setters for line/column. */
/* ... */
public boolean hetAttribute(NodeAttribute attribute) {
return this.additionalAttributes.containsKey(attribute);
}
public <T> T getAttributeValue(NodeAttribute attribute, Class<T> attributeClass) {
Object attributeValue = this.additionalAttributes.get(attribute);
// You may want to wrap the ClassCastException that may be raisen here to a more specfic error
T castedAttributeValue = attributeClass.cast(attributeValue);
return castedAttributeValue;
}
public void setAttributeValue(NodeAttribute attribute, Object value) {
// Notice that this implemintation allows changing the type of an existing attribute,
// If this is invalid behavior in your case you can throw an exception instead
this.additionalAttributes.put(attribute, value);
}
}
// Example usage
public class Program {
public static void main(String[] args) {
Node nodeWithNameOnly = new Node();
nodeWithNameOnly.setAttributeValue(NodeAttribute.NAME, 'node1');
Node nodeWithBoth = new Node();
nodeWithBoth.setAttributeValue(NodeAttribute.NAME, 'node2');
nodeWithBoth.setAttributeValue(NodeAttribute.ACCESSIBILTY, NodeAccessibility.PRIVATE);
Program.doStuffWithNode(nodeWithNameOnly);
/* output:
Node name: node1
*/
Program.doStuffWithNode(nodeWithBoth);
/* output:
Node name: node2
Node is public: False
*/
}
public static void doStuffWithNode(Node node) {
if (nodeWithNameOnly.hetAttribute(NodeAttribute.NAME)) {
String nodeName = nodeWithNameOnly.getAttributeValue(NodeAttribute.NAME, String.class);
system.out.println("Node name: " + nodeName);
}
if (nodeWithNameOnly.hetAttribute(NodeAttribute.ACCESSIBILTY)) {
NodeAccessibility nodeAccessibilty =
nodeWithNameOnly.getAttributeValue(NodeAttribute.ACCESSIBILTY, NodeAccessibility.class);
boolean nodeIsPublic = nodeAccessibilty == NodeAccessibility.PUBLIC;
system.out.println("Node is public: " + String.valueOf(nodeIsPublic));
}
}
}
In any case, this is the main rule of thumb - Inheritance should be used for an "is a" relation, whereas composition should be used for an "has a" relation.
For instance:
Fish extends Animal because a Fish is an Animal.
Post holds comments because a Post has comments.
And in our case, a node has a name and an accessibility level so it should hold them.
Currently I have several enums defined over several classes. They all look similar to the one shown below:
public class ApaMessage {
private String apaMessage;
private final int FIXED_LENGTH_SIZE=39;
public enum ApaFields {
FIELD1(ApaUtils.ApaFieldTypes.POSITION_BASED, null, "field1", 2, 3, false, false),
private final ApaUtils.ApaFieldTypes type;
private final String ApaName;
private final String jsonName;
private final int start;
private final int finish;
private boolean required = false;
private boolean withDelimiter = false;
ApaFields(ApaUtils.ApaFieldTypes type, String ApaName, String jsonName, int start, int finish, boolean required, boolean withDelimiter) {
this.type = type;
this.ApaName = ApaName;
this.jsonName = jsonName;
this.start = start;
this.finish = finish;
this.required = required;
this.withDelimiter = withDelimiter;
}
}
There is also a method defined in ApaMessage:
private HashMap<String,Object> getApaJsonFieldsAndValues() {
HashMap<String, Object> jsonApaData = new HashMap<String, Object>();
for (ApaFields field : ApaFields.values()) {
jsonApaData.put(field.jsonName, getApaFieldValue(field));
}
return jsonApaData;
}
The problem is although there isn't a lot of code, I will soon have 10-20 of these enums. I would like to create an abstract base class where the HashMap method, and other similar methods can be part of. The base class should accept an ApaFields enum and other enums and do what the getApaJsonFieldsAndValues does. The problem is, how can the base class access the passed enum values and the internal fields such as jsonName to do the loop?
I have tried different approaches but the main problem is that the base class cannot seem to access the values. Is there any way around this? Alternatively, is there a better approach? Thanks
EDIT:
Basically I would like something like this in the base class. Note the below doesn't compile.
public abstract class ApaRequestMessage {
private Class<? extends Enum<?>> apaRequestMessageFields;
private String apaMessage;
public <T extends Enum<T>> void ApaRequest(Object apaRequestFields, String apaMessage) {
apaRequestMessageFields = (Class<? extends Enum<?>>) apaRequestFields;
this.apaMessage = apaMessage;
for (Field field: apaRequestMessageFields.values()) {
//this doesn't work because it cannot access the values of apaRequestMessageFields
}
}
}
And then call the base method as follows, although not sure if this is correct, where ApaFields is the inner enum defined above.
ApaRequest(ApaFields.class, somestringmessage);
I came across something similar when trying to define a db schema using enums as columns in the table. I eventually took this route.
Define a base class with sufficient generic signature to ensure the enum is properly built.
public class Table<Column extends Enum<? extends Column>> {
// Name of the table.
protected final String tableName;
// All of the columns in the table. This is actually an EnumSet so very efficient.
protected final Set<Column> columns;
/**
* The base interface for all Column enums.
*/
public interface Columns {
// What type does it have in the database?
public Type getType();
}
// Small list of database types.
public enum Type {
String, Number, Date;
}
public Table(String tableName,
Set<Column> columns) {
this.tableName = tableName;
this.columns = columns;
}
}
Now extend this for each table - here is a simple VersionTable:
public class VersionTable extends Table<VersionTable.Column> {
public enum Column implements Table.Columns {
Version(Table.Type.String),
ReleaseDate(Table.Type.Date);
final Table.Type type;
Column(Table.Type type) {
this.type = type;
}
#Override
public Type getType() {
return type;
}
}
public VersionTable() {
super("Versions", EnumSet.allOf(Column.class));
}
}
Now you have all of the core functionality in the base class and all the sub-classes need to do is implement the interface on the enum.
I realise this does not address the issue of duplicated bolierplate code in all of your enums but it does move alomst all of it elsewhere.
I'm writing a library, which has a predefined set of values for an enum.
Let say, my enum looks as below.
public enum EnumClass {
FIRST("first"),
SECOND("second"),
THIRD("third");
private String httpMethodType;
}
Now the client, who is using this library may need to add few more values. Let say, the client needs to add CUSTOM_FIRST and CUSTOM_SECOND. This is not overwriting any existing values, but makes the enum having 5 values.
After this, I should be able to use something like <? extends EnumClass> to have 5 constant possibilities.
What would be the best approach to achieve this?
You cannot have an enum extend another enum, and you cannot "add" values to an existing enum through inheritance.
However, enums can implement interfaces.
What I would do is have the original enum implement a marker interface (i.e. no method declarations), then your client could create their own enum implementing the same interface.
Then your enum values would be referred to by their common interface.
In order to strenghten the requirements, you could have your interface declare relevant methods, e.g. in your case, something in the lines of public String getHTTPMethodType();.
That would force implementing enums to provide an implementation for that method.
This setting coupled with adequate API documentation should help adding functionality in a relatively controlled way.
Self-contained example (don't mind the lazy names here)
package test;
import java.util.ArrayList;
import java.util.List;
public class Main {
public static void main(String[] args) {
List<HTTPMethodConvertible> blah = new ArrayList<>();
blah.add(LibraryEnum.FIRST);
blah.add(ClientEnum.BLABLABLA);
for (HTTPMethodConvertible element: blah) {
System.out.println(element.getHTTPMethodType());
}
}
static interface HTTPMethodConvertible {
public String getHTTPMethodType();
}
static enum LibraryEnum implements HTTPMethodConvertible {
FIRST("first"),
SECOND("second"),
THIRD("third");
String httpMethodType;
LibraryEnum(String s) {
httpMethodType = s;
}
public String getHTTPMethodType() {
return httpMethodType;
}
}
static enum ClientEnum implements HTTPMethodConvertible {
FOO("GET"),BAR("PUT"),BLAH("OPTIONS"),MEH("DELETE"),BLABLABLA("POST");
String httpMethodType;
ClientEnum(String s){
httpMethodType = s;
}
public String getHTTPMethodType() {
return httpMethodType;
}
}
}
Output
first
POST
Enums are not extensible. To solve your problem simply
turn the enum in a class
create constants for the predefined types
if you want a replacement for Enum.valueOf: track all instances of the class in a static map
For example:
public class MyType {
private static final HashMap<String,MyType> map = new HashMap<>();
private String name;
private String httpMethodType;
// replacement for Enum.valueOf
public static MyType valueOf(String name) {
return map.get(name);
}
public MyType(String name, String httpMethodType) {
this.name = name;
this.httpMethodType = httpMethodType;
map.put(name, this);
}
// accessors
public String name() { return name; }
public String httpMethodType() { return httpMethodType; }
// predefined constants
public static final MyType FIRST = new MyType("FIRST", "first");
public static final MyType SECOND = new MyType("SECOND", "second");
...
}
Think about Enum like a final class with static final instances of itself. Of course you cannot extend final class, but you can use non-final class with static final instances in your library. You can see example of this kind of definition in JDK. Class java.util.logging.Level can be extended with class containing additional set of logging levels.
If you accept this way of implementation, your library code example can be like:
public class EnumClass {
public static final EnumClass FIRST = new EnumClass("first");
public static final EnumClass SECOND = new EnumClass("second");
public static final EnumClass THIRD = new EnumClass("third");
private String httpMethodType;
protected EnumClass(String name){
this.httpMethodType = name;
}
}
Client application can extend list of static members with inheritance:
public final class ClientEnum extends EnumClass{
public static final ClientEnum CUSTOM_FIRST = new ClientEnum("custom_first");
public static final ClientEnum CUSTOM_SECOND = new ClientEnum("custom_second");
private ClientEnum(String name){
super(name);
}
}
I think that this solution is close to what you have asked, because all static instances are visible from client class, and all of them will satisfy your generic wildcard.
We Fixed enum inheritance issue this way, hope it helps
Our App has few classes and each has few child views(nested views), in order to be able to navigate between childViews and save the currentChildview we saved them as enum inside each Class.
but we had to copy paste, some common functionality like next, previous and etc inside each enum.
To avoid that we needed a BaseEnum, we used interface as our base enum:
public interface IBaseEnum {
IBaseEnum[] getList();
int getIndex();
class Utils{
public IBaseEnum next(IBaseEnum enumItem, boolean isCycling){
int index = enumItem.getIndex();
IBaseEnum[] list = enumItem.getList();
if (index + 1 < list.length) {
return list[index + 1];
} else if(isCycling)
return list[0];
else
return null;
}
public IBaseEnum previous(IBaseEnum enumItem, boolean isCycling) {
int index = enumItem.getIndex();
IBaseEnum[] list = enumItem.getList();
IBaseEnum previous;
if (index - 1 >= 0) {
previous = list[index - 1];
}
else {
if (isCycling)
previous = list[list.length - 1];
else
previous = null;
}
return previous;
}
}
}
and this is how we used it
enum ColorEnum implements IBaseEnum {
RED,
YELLOW,
BLUE;
#Override
public IBaseEnum[] getList() {
return values();
}
#Override
public int getIndex() {
return ordinal();
}
public ColorEnum getNext(){
return (ColorEnum) new Utils().next(this,false);
}
public ColorEnum getPrevious(){
return (ColorEnum) new Utils().previous(this,false);
}
}
you could add getNext /getPrevious to the interface too
#wero's answer is very good but has some problems:
the new MyType("FIRST", "first"); will be called before map = new HashMap<>();. in other words, the map will be null when map.add() is called. unfortunately, the occurring error will be NoClassDefFound and it doesn't help to find the problem. check this:
public class Subject {
// predefined constants
public static final Subject FIRST;
public static final Subject SECOND;
private static final HashMap<String, Subject> map;
static {
map = new HashMap<>();
FIRST = new Subject("FIRST");
SECOND = new Subject("SECOND");
}
private final String name;
public Subject(String name) {
this.name = name;
map.put(name, this);
}
// replacement for Enum.valueOf
public static Subject valueOf(String name) {
return map.get(name);
}
// accessors
public String name() {
return name;
}
I have a couple of objects from which selected members should be combined to create an output object. All these are POJOs. I am seeing that all object mappers work on a single POJO to another POJO level. Is there any mapper that supports what I am looking for? Of course, I understand that there is some mapping stuff that I need to specify.
Edit:
I know how to get this done by writings own Java class. I am just looking for a way to do it with one of the mapping libraries.
You aren't limited in what you require to be passed to your mapper. You can define it to accept several items and build the object based on the multiple inputs. Here is an example:
public class ClassOne {
private final String someProperty;
public ClassOne(String someProperty) {
this.someProperty = someProperty;
}
public String getSomeProperty() {
return someProperty;
}
}
public class ClassTwo {
private final String someOtherProperty;
public ClassTwo(String someOtherProperty) {
this.someOtherProperty = someOtherProperty;
}
public String getSomeOtherProperty() {
return someOtherProperty;
}
}
public class CombinedClass {
public static CombinedClass mapper(ClassOne one, ClassTwo two){
return new CombinedClass(one.getSomeProperty(), two.getSomeOtherProperty());
}
private final String someProperty;
private final String someOtherProperty;
private CombinedClass(String someProperty, String someOtherProperty) {
this.someProperty = someProperty;
this.someOtherProperty = someOtherProperty;
}
public String getSomeProperty() {
return someProperty;
}
public String getSomeOtherProperty() {
return someOtherProperty;
}
}
CLARIFICATION:
I do not know the objects name. That is where the problem comes in. I am creating an object like such:
`new Object(String attributes);
I am trying to run code in another class such as:
***.getStuff();
the trick to it is, there is no name for the Object. but i do know what String attributes is
The question: Is there any way to accomplish this without using the dreaded for loop?
This question is a bit tricky to word, but I will try my best. What I want to is get an object that matches a particular field without making a messy for loop. Something along the lines of:
Object A has the field String name.
String nameObj = "Tickle";
Object A has the name "Tickle"
if(nameObj.equals(Object A)){
//bla bla
}
Very confusing wording, yes. Sorry about that. I want to use Object A in my code without having to figure out which object it is, assuming all I have is its name. I am looking for a shortcut around using a for loop, I suppose.
Feel free to ask questions about what I am looking for. Sorry about the terribly worded question.
Poor coding, but this is what I am looking for...
nameObj.getName().getObjectA();
If you have a bunch of objects with names, and you want to grab an object by its name, I suggest you look up the class HashMap. HashMap lets you put in objects under keys, and when you give the hash map a key it returns the object associated with that key. So in your example, the keys would be string names.
Take at this implementation, that demonstrates what #Patashu said, create a map to the objects, in this case I just add an abstract class at the top of all.
import java.util.HashMap;
public class FindMeBaby {
public static void main(String[] args) {
Factory.add(new NiceGuy("first one"));
Factory.add(new FirstChild("ok im late"));
System.out.println(Factory.get("first one")
.getVeryImportantInformationThatOnlyThisClassKnows());
}
}
abstract class ParentOfAll {
protected String id;
public ParentOfAll(String id) {
this.id = id;
}
public String getId(){
return id;
}
public abstract String getVeryImportantInformationThatOnlyThisClassKnows();
}
class FirstChild extends ParentOfAll {
public FirstChild(String id) {
super(id);
}
public String getVeryImportantInformationThatOnlyThisClassKnows() {
return "this is a secret";
}
}
class NiceGuy extends ParentOfAll {
public NiceGuy(String id) {
super(id);
}
public String getVeryImportantInformationThatOnlyThisClassKnows() {
return "to say the true, i'm not that nice :)";
}
}
class Factory {
private static HashMap allTheObjects = new HashMap();
public static Object add(ParentOfAll object) {
allTheObjects.put(object.getId(), object);
return object;
}
public static ParentOfAll get(String key) {
return (ParentOfAll) allTheObjects.get(key);
}
}
This is another version, of the same implementation with a more transparent aproach, without the Factory class, the Parent itself will keep track of the instances and save in a list.
import java.util.HashMap;
public class FindMeBaby {
public static void main(String[] args) {
NiceGuy foo = new NiceGuy("first one");
FirstChild bar = new FirstChild("ok im late");
System.out.println(ParentOfAll.get("first one")
.getVeryImportantInformationThatOnlyThisClassKnows());
}
}
abstract class ParentOfAll {
protected String id;
public ParentOfAll(String id) {
this.id = id;
add(this);
}
public String getId() {
return id;
}
public abstract String getVeryImportantInformationThatOnlyThisClassKnows();
private static HashMap allTheObjects = new HashMap();
private static Object add(ParentOfAll object) {
allTheObjects.put(object.getId(), object);
return object;
}
public static ParentOfAll get(String key) {
return (ParentOfAll) allTheObjects.get(key);
}
}
class FirstChild extends ParentOfAll {
public FirstChild(String id) {
super(id);
}
public String getVeryImportantInformationThatOnlyThisClassKnows() {
return "this is a secret";
}
}
class NiceGuy extends ParentOfAll {
public NiceGuy(String id) {
super(id);
}
public String getVeryImportantInformationThatOnlyThisClassKnows() {
return "to say the true, i'm not that nice :)";
}
}