Related
I have an object "JudgesSubmission" with the following methods:
public String getInnovationGrade1() {
return innovationGrade1;
}
public String getInnovationGrade2() {
return innovationGrade2;
}
public String getInnovationGrade3() {
return innovationGrade3;
}
public String getInnovationGrade4() {
return innovationGrade4;
}
Now, when calling these methods, I want to put them in a loop where the called method name gets the index of the loop attached to its end changing the method called. Is this possible?
For example, the following code would never work, but I am writing it to explain what I need:
judgesSubmission metricScores= new judgesSubmission;
int metricSum=0;
for (int i=0;i<4;i++){
metricSum=metricSum
Integer.parseInt(metricScores.getInnovationGrade+"i"());
}
Is there a way to do that or do I always have the full method name written?
What you want to do is not possible... but with reflection such as :
MyObject.class.getMethod("mymethod"+i);
Without reflection you could use a Supplier<String> :
public void process(Supplier<String>... suppliers){
judgesSubmission metricScores= new judgesSubmission;
int metricSum=0;
for (Supplier<String> supplier : suppliers){
Integer.parseInt(supplier.get());
}
}
And call it such as :
MyObject myObject = new MyObject();
process(()->myObject.getInnovationGrade1(),
()->myObject.getInnovationGrade2(),
()->myObject.getInnovationGrade3(),
()->myObject.getInnovationGrade4());
It is not possible without reflection (and is highly not recommended)
Instead you may want to use other methods:
An array of the data (either replacing the 4 methods, or in addition)
String[] getInnovationGrades()
{
return new String[]{innovationGrade1, innovationGrade2, innovationGrade3, innovationGrade4};
}
Then later you can use
for(String innovationGrade : getInnovationGrades())
//do stuff
An argument to get the data you want
String getInnovationGrade(int i)
{
switch(i)
{
case 1:
return getInnovationGrade1();
case 2:
return getInnovationGrade2();
case 3:
return getInnovationGrade3();
case 4:
return getInnovationGrade4();
default:
return ""; //or throw exception, depends on how you wish to handle errors
}
}
Then later you can use
for(int i = 1; i <= 4; i++)
getInnovationGrade(i); //and do stuff with it
I wrote a library
This library accept the limited options and print the related string.
public class Lib {
public enum Num {
ZERO,
ONE,
TWO,
THREE
}
public static void main(String[] args) {
Lib obj = new Lib();
obj.print(Num.ONE);
}
public void print(Num num) {
switch (num) {
case ZERO:
System.out.println("ZERO is "+Num.ZERO.ordinal());
break;
case ONE:
System.out.println("ONE is "+Num.ONE.ordinal());
break;
case TWO:
System.out.println("TWO is "+Num.TWO.ordinal());
break;
case THREE:
System.out.println("THREE is "+Num.THREE.ordinal());
break;
default:
break;
}
}
}
In the new version, I will disable option ONE and TWO
public enum Num {
ZERO,
//ONE,
//TWO,
THREE
}
How can I keep the correct values after I disabled the options?
It is not clear what you are asking. If you change any piece of code and thereby "remove" "names" that formerly existed ... than of course, any "reference" to any of the deleted elements is ... first of all: broken.
In case of an enum, you might prefer to not rely on build-in ordinals; instead you could go for this:
enum Whatever {
ONE(1), TWO(2);
private final int value;
private Whatever(value) {
this.value = value;
}
public int getValue() { return value }
But you have to be really careful here. For example, if you are persisting enum objects (into some sort of database for example) then any such change (adding or removing enum "values") will lead to incompatibilities!
I am not sure of what you want to do, but for example you can do this:
public enum Num {
ZERO,
ONE,
TWO,
THREE
}
switch (num) {
case ZERO:
System.out.println("ZERO is "+Num.ZERO.ordinal());
break;
case THREE:
System.out.println("ZERO is "+Num.THREE.ordinal());
break;
case One:
case Two:
default:
break;
You might be disable some of enum now onward and keep stored as it is. To support both the things, you should have a method that returns list of enum that will populate on UI. I.E. List getPopulatedOnUi(). That contains those enum list that you needed.
Don't remove from definition itself. keep as it is. because that will throw error for existing as it might be stored into database.
You can modify the print() method as below: Instead of switch, you can use for loop and make the code little bit generic. Now, even when your enum values changes, you need not to make any changes in this code.
It will handle the case , If you disable some enum values in future.
public void print(Num num) {
for(Num n : Num.values()) {
if(n == num) {
System.out.println(n.name()+ " is " + n.ordinal());
break;
}
}
}
As a fairly green Java coder I've set myself the hefty challenge of trying to write a simple text adventure. Unsurprisingly, I've encountered difficulties already!
I'm trying to give my Location class a property to store which exits it contains. I've used a boolean array for this, to essentially hold true/false values representing each exit. I'm not entirely convinced that
a) this is the most efficient way to do this and
b) that I'm using the right code to populate the array.
I would appreciate any and all feedback, even if it is for a complete code over-haul!
At present, when instantiating a Location I generate a String which I send through to the setExits method:
String e = "N S U";
secretRoom.setExits(e);
In the Location class, setExits looks like this:
public void setExits(String e) {
if (e.contains("N"))
bexits[0] = true;
else if (e.contains("W"))
bexits[1] = true;
else if (e.contains("S"))
bexits[2] = true;
else if (e.contains("E"))
bexits[3] = true;
else if (e.contains("U"))
bexits[4] = true;
else if (e.contains("D"))
bexits[5] = true;
}
I'll be honest, I think this looks particularly clunky, but I couldn't think of another way to do it. I'm also not entirely sure now how to write the getExits method...
Any help would be welcome!
The most efficient and expressive way is the following:
Use enums as Exits and use an EnumSet to store them. EnumSet is an efficient Set implementation that uses a bit field to represent the enum constants.
Here is how you can do it:
public enum Exit { North, West, South, East, Up, Down; }
EnumSet<Exit> set = EnumSet.noneOf(Exit.class); // An empty set.
// Now you can simply add or remove exits, everything will be stored compactly
set.add(Exit.North); // Add exit
set.contains(Exit.West); // Test if an exit is present
set.remove(Exit.South); //Remove an exit
Enum set will store all exits in a single long internally, so your code is expressive, fast, and saves a lot of memory.
Is there any reason why you are doing this with Strings and aren't passing in booleans, i.e.
public void setExits(boolean N, boolean E, boolean S, boolean W, boolean U, boolean D)
Or having setters?
public void setNorthOpen(boolean open)
{
bexits[4] = open;
}
Secondly, why are you storing the exits as an array of booleans, it's a small finite set, why not just
boolean N,S,E,W,U,D;
As then you don't need to keep track of which number in the array each direction is.
Also
This is a correct answer (if not completely optimal like that of #gexicide) but I fully encourage anyone to look at the other answers here for an interesting look at how things can be done in Java in different ways.
For future reference
Code which works belongs on Code Review, not Stack Overflow. Although as #kajacx pointed out, this code shouldn't -in fact- work.
OK, first of all, your setExits() method will not work as intended, chained if-elseif will maximally execute 1 branch of code, for example:
if (e.contains("N"))
bexits[0] = true;
else if (e.contains("W"))
bexits[1] = true;
Even if e contains both N and W, only bexits[0] will be set. Also this method will only add exits (for example calling setExits("") will not delete any existing exits.
I would change that method to:
bexits[0] = e.contains("N");
bexits[1] = e.contains("W");
...
Also, i definetly wouldn't remember that north is on index 0, west in on 1, ... so a common practice is to name your indexes using final static constants:
public static final int NORTH = 0;
public static final int WEST = 1;
...
Then you can write in your setExits method:
bexits[NORTH] = e.contains("N");
bexits[WEST] = e.contains("W");
...
(much more readible)
Finally, if you want your code even more well-arranged, you can make a Exits class representing avaliable exits, and backed by boolean array. Then on place where you create your String, you could create this class instead and save yourself work with generating and then parsing a string.
EDIT:
as #gexicide answers, there is a really handy class EnumSet which would be probably better for representing the exits than bollean array.
The EnumSet in the other answer is the best way to do this, I just wanted to add one more thing though for the future when you start looking not just at whether you can move but where you are moving to.
As well as EnumSet you also have EnumMap.
If you define a Room class/interface then inside the Room class you can have
Map<Direction, Room> exits = new EnumMap<>(Direction.class);
You can now add your links into the map as follows:
exits.put(Direction.NORTH, theRoomNorthOfMe);
Then your code to move between rooms can be very general purpose:
Room destination=currentRoom.getExit(directionMoved);
if (destination == null) {
// Cannot move that way
} else {
// Handle move to destination
}
I would create an Exit enum and on the location class just set a list of Exit objects.
so it would be something like:
public enum Exit { N, S, E, W, U, D }
List<Exit> exits = parseExits(String exitString);
location.setExits(exits);
Given what your code looks like, this is the most readable implementation I could come up with:
public class Exits {
private static final char[] DIRECTIONS = "NSEWUD".toCharArray();
public static void main(String... args) {
String input = "N S E";
boolean[] exits = new boolean[DIRECTIONS.length];
for(int i = 0; i< exits.length; i++) {
if (input.indexOf(DIRECTIONS[i]) >= 0) {
exits[i] = true;
}
}
}
}
That being said, there's a number of cleaner solutions possible. Personally I would go with enums and an EnumSet.
By the way, your original code is incorrect, as it will set as most one value in the array to true.
If you're defining exits as a string, you should use it. I would do it like:
public class LocationWithExits {
public static final String NORTH_EXIT="[N]";
public static final String SOUTH_EXIT="[S]";
public static final String EAST_EXIT="[E]";
public static final String WEST_EXIT="[W]";
private final String exitLocations;
public LocationWithExits(String exitLocations) {
this.exitLocations = exitLocations;
}
public boolean hasNorthExit(){
return exitLocations.contains(NORTH_EXIT);
}
public static void main(String[] args) {
LocationWithExits testLocation=new LocationWithExits(NORTH_EXIT+SOUTH_EXIT);
System.out.println("Has exit on north?: "+testLocation.hasNorthExit());
}
}
using array of booleans might cause a lot of problems if you forget what exactly means bexits[0]. Os it for north or south? etc.
or you can just use enums and list of exits available . Then in methid test if list contain a certain enum value
Personally, I think you can hack it around a bit using an enum and turn the following:
public void setExits(String e) {
if (e.contains("N"))
bexits[0] = true;
else if (e.contains("W"))
bexits[1] = true;
else if (e.contains("S"))
bexits[2] = true;
else if (e.contains("E"))
bexits[3] = true;
else if (e.contains("U"))
bexits[4] = true;
else if (e.contains("D"))
bexits[5] = true;
}
into
public enum Directions
{
NORTH("N"),
WEST("W"),
SOUTH("S"),
EAST("E"),
UP("U"),
DOWN("D");
private String identifier;
private Directions(String identifier)
{
this.identifier = identifier;
}
public String getIdentifier()
{
return identifier;
}
}
and then do:
public void setExits(String e)
{
String[] exits = e.split(" ");
for(String exit : exits)
{
for(Directions direction : Directions.values())
{
if(direction.getIdentifier().equals(exit))
{
bexits[direction.ordinal()] = true;
break;
}
}
}
}
Although after having written it down, I can't really tell you if it's that much better. It's easier to add new directions, that's for sure.
All the approaches listed in the answeres are good. But I think the approach you need to take depends on the way you are going to use the exit field. For example if you are going to handle exit as strings then Ross Drews approach would require a lot of if-else conditions and variables.
String exit = "N E";
String[] exits = exit.split(" ");
boolean N = false, E = false, S = false, W = false, U = false, D = false;
for(String e : exits){
if(e.equalsIgnoreCase("N")){
N = true;
} else if(e.equalsIgnoreCase("E")){
E = true;
} else if(e.equalsIgnoreCase("W")){
W= true;
} else if(e.equalsIgnoreCase("U")){
U = true;
} else if(e.equalsIgnoreCase("D")){
D = true;
} else if(e.equalsIgnoreCase("S")){
S = true;
}
}
setExits(N, E, S, W, U, D);
Also if you have an exit and you want to check whether a location has that particular exit then again you will have to do the same
public boolean hasExit(String exit){
if(e.equalsIgnoreCase("N")){
return this.N; // Or the corresponding getter method
} else if(e.equalsIgnoreCase("E")){
return this.E;
} else if(e.equalsIgnoreCase("W")){
return this.W;
} else if(e.equalsIgnoreCase("U")){
return this.U;
} else if(e.equalsIgnoreCase("D")){
return this.D;
} else if(e.equalsIgnoreCase("S")){
return this.S;
}
}
So if you are going to manipulate it as a string, in my opinion the best approach would be to go for list and enum. By this way you could do methods like hasExit, hasAnyExit, hasAllExits, hasNorthExit, hasSouthExit, getAvailableExits etc etc.. very easily. And considering the number of exits (6) using a list (or set) wont be an overhead. For example
Enum
public enum EXIT {
EAST("E"),
WEST("W"),
NORTH("N"),
SOUTH("S"),
UP("U"),
DOWN("D");
private String exitCode;
private EXIT(String exitCode) {
this.exitCode = exitCode;
}
public String getExitCode() {
return exitCode;
}
public static EXIT fromValue(String exitCode) {
for (EXIT exit : values()) {
if (exit.exitCode.equalsIgnoreCase(exitCode)) {
return exit;
}
}
return null;
}
public static EXIT fromValue(char exitCode) {
for (EXIT exit : values()) {
if (exit.exitCode.equalsIgnoreCase(String.valueOf(exitCode))) {
return exit;
}
}
return null;
}
}
Location.java
import java.util.ArrayList;
import java.util.List;
public class Location {
private List<EXIT> exits;
public Location(){
exits = new ArrayList<EXIT>();
}
public void setExits(String exits) {
for(char exitCode : exits.toCharArray()){
EXIT exit = EXIT.fromValue(exitCode);
if(exit != null){
this.exits.add(exit);
}
}
}
public boolean hasExit(String exitCode){
return exits.contains(EXIT.fromValue(exitCode));
}
public boolean hasAnyExit(String exits){
for(char exitCode : exits.toCharArray()){
if(this.exits.contains(EXIT.fromValue(exitCode))){
return true;
}
}
return false;
}
public boolean hasAllExit(String exits){
for(char exitCode : exits.toCharArray()){
EXIT exit = EXIT.fromValue(exitCode);
if(exit != null && !this.exits.contains(exit)){
return false;
}
}
return true;
}
public boolean hasExit(char exitCode){
return exits.contains(EXIT.fromValue(exitCode));
}
public boolean hasNorthExit(){
return exits.contains(EXIT.NORTH);
}
public boolean hasSouthExit(){
return exits.contains(EXIT.SOUTH);
}
public List<EXIT> getExits() {
return exits;
}
public static void main(String args[]) {
String exits = "N E W";
Location location = new Location();
location.setExits(exits);
System.out.println(location.getExits());
System.out.println(location.hasExit('W'));
System.out.println(location.hasAllExit("N W"));
System.out.println(location.hasAnyExit("U D"));
System.out.println(location.hasNorthExit());
}
}
Why not this if you want a shorter code:
String symbols = "NWSEUD";
public void setExits(String e) {
for (int i = 0; i < 6; i++) {
bexits[i] = e.contains(symbols.charAt(i));
}
}
If you want a generic solution you can use a map, which maps from a key (in your case W, S, E.. ) to a corresponding value (in your case a boolean).
When you do a set, you update the value the key is associated with. When you do a get, you can take an argument key and simply retrieve the value of the key. This functionality does already exist in map, called put and get.
I really like the idea of assigning the exits from a String, because it makes for brief and readable code. Once that's done, I don't see why you would want to create a boolean array. If you have a String, just use it, although you might want to add some validation to prevent accidental assignment of strings containing unwanted characters:
private String exits;
public void setExits(String e) {
if (!e.matches("[NSEWUD ]*")) throw new IllegalArgumentException();
exits = e;
}
The only other thing I would add is a method canExit that you can call with a direction parameter; e.g., if (location.canExit('N')) ...:
public boolean canExit(char direction) {
return exits.indexOf(direction) >= 0;
}
I like enums, but using them here seems like over-engineering to me, which will rapidly become annoying.
**Edit**: Actually, don't do this. It answers the wrong question, and it does something which doesn't need to be done. I just noticed #TimB's answer of using a map (an EnumMap) to associate directions with rooms. It makes sense.
I still feel that if you only need to track exit existence, a String is simple and effective, and anything else is over-complicating it. However, only knowing which exits are available isn't useful. You will want to go through those exits, and unless your game has a very plain layout it won't be doable for the code to infer the correct room for each direction, so you'll need to explicitly associate each direction with another room. So there seems to be no actual use for any method "setExits" which accepts a list of directions (regardless of how it's implemented internally).
public void setExits(String e)
{
String directions="NwSEUD";
for(int i=0;i<directions.length();i++)
{
if(e.contains(""+directions.charAt(i)))
{
bexits[i]=true;
break;
}
}
}
the iterative way of doing the same thing..
Long chains of else if statements should be replaced with switch statements.
Enums are the most expressive way to store such values as long as the efficiency is not a concern. Keep in mind that enum is a class, so creation of a new enum is associated with corresponding overhead.
I'm beginner at java, and I'm making a simple program where I type in something, and if what I type in matches one of the things on the "database" then it'll print some text. Is there a simpler way to check this rather than doing this:
int 1;
int 2;
int 3;
etc.
if([USER INPUT].equals("1")) {
System.out.println("TEST");
}
400 times.
Use a switch statement or a HashMap.
Switch statement: Readable, but compiles similarly (if not identically) to an if-else chain.
switch([USER_INPUT]) {
case 1:
System.out.println("TEST");
break;
case 2:
System.out.println("HELLO");
break;
// And so on.
}
Hash Map: Much more readable and simpler. This is preferred.
// Initialization.
Map<Integer,String> map = new HashMap<Integer,String>();
map.put(1,"TEST");
map.put(2,"HELLO");
// Printing.
String s = map.get(USER_INPUT);
if (s == null)
System.out.println("Key doesn't exist.");
System.out.println(s);
Use a HashMap, with key as Integer, and value as text.
System.out.println(myMap.get(USER_INPUT));
Where you have done myMap.put(1, "TEST"); etc, this keeps your code much OO.
the underlying bytecode of switch and if are very comparable, and personally don't see any advantage of switching to switch (unless you want fall through, which means don't include break statement).
A fun alternative would be to use an enum. This would work if you want to define all of the values in a class. It would simplify the code used to get the text value. And it gives you some more fun options beyond what a switch statement would give you.
enum NumberText {
HELLO(1),
WORLD(2);
private static final HashMap<Integer,NumberText> map = new HashMap<Integer,NumberText>();
static{
for (ConnectionGenerator c : ConnectionGenerator.values()) {
map.put(c.code, c);
}
}
Integer code;
NumberText(Integer pCode) {
this.code = pCode;
}
Static ConnectionGenerator getTextFor(Integer code) {
return map.get(code);
}
}
Then to get the text, simply do this:
NumberText nt = NumberText.getTextFor(USER_INPUT);
System.out.println(nt);
You can get fancier and put an additional constructor variable into the enum and have a specific string of text.
enum NumberText {
HELLO(1, "Hello to You"),
GOODBYE(2, "Goodbye");
private static final HashMap<Integer,NumberText> map = new HashMap<Integer,NumberText>();
static{
for (ConnectionGenerator c : ConnectionGenerator.values()) {
map.put(c.code, c);
}
}
Integer code;
String text;
NumberText(Integer pCode, String pText) {
this.code = pCode;
this.text = pText;
}
ConnectionGenerator getNumberTextFor(Integer code) {
return map.get(code);
}
getText() {
return this.text;
}
}
Then you could get the text like this:
NumberText.getNumberTextFor(USER_INPUT).getText();
Use a switch statement.
switch(i){
case 1:
System.out.println("Hi");
break;
case 2:
System.out.println("Ok");
break;
// ...
}
You can use a switch statement.
Here's a quick tutorial and some more in-depth explanation.
http://docs.oracle.com/javase/tutorial/java/nutsandbolts/switch.html
How can I improve this?
The relationship is one to one and continuous on [-1,5] so i was thinking of using enum, but I'm not sure how to compare a string value to an enum value.
If there is any better way to do this, please suggest.
Thanks!
private int evaluateWord(String sval) {
if (sval.equals("program"))
return 1;
else if (sval.equals("begin"))
return 2;
else if (sval.equals("end"))
return 3;
else if (sval.equals("int"))
return 4;
else if (sval.equals("if"))
return 5;
else
System.exit(0);
Have you considered stuffing the mapping into a HashMap once, and then just querying the map?
For example, something like this:
private static final Map<String,Integer> m_map = new HashMap<String,Integer>();
static {
m_map.put( "program", 1 );
m_map.put( "begin", 2 );
m_map.put( "end", 3 );
m_map.put( "int", 4 );
m_map.put( "if", 5 );
}
private int evaluateWord(String sval) {
Integer value = m_map.get( sval );
if ( null != value ) {
return value;
}
else {
System.exit(0);
}
}
By the way, it looks as if you're writing a parser. It can be reasonable to write a parser by hand. Another option to consider, unless you have a good reason to write it by hand, is a parser generator like ANTLR.
Using an enumeration:
enum Word {
PROGRAM(1,"program"),
BEGIN(2,"begin"),
END(3,"end"),
INT(4,"int"),
IF(5,"if");
private final int value;
private final String representation;
Word(int value, String representation)
{
this.value = value;
this.representation = representation;
}
public int value()
{ return value; }
private static Map<String, Word> fromRep =
new HashMap<String, EnumExample2.Word>();
public static Word fromRepresentation(String rep) {
if (!validRep(rep)) {
throw new IllegalArgumentException("No rep: "+rep);
}
return fromRep.get(rep);
}
public static boolean validRep(String rep)
{ return fromRep.get(rep) != null; }
static {
for (Word word : Word.values()) {
fromRep.put(word.representation, word);
}
}
}
Then your logic is:
private int evaluateWord(String sval) {
if (!Word.validRep(sval)) {
System.exit(0);
}
return Word.fromRepresentation(sval).value();
}
A hashmap could work:
private static HashMap<String, Integer> lookup = new HashMap<String, Integer>();
static {
lookup.put("program", 1);
lookup.put("being", 2);
lookup.put("end", 3);
lookup.put("int", 4);
lookup.put("if", 5);
}
private int evaluateWord(String sval) {
if ( lookup.containsKey(sval) ) {
return lookup.get(sval);
}
System.exit(0);
}
This is what a map is for;
Create a HashMap, add key and values to the map like
wordMap.put("program", Integer.valueOf(1));
....
then, to get the value do
Integer val = wordMap.get(sval);
Honestly, I wouldn't worry about keeping something like this ultra efficient, but there is a change you could make. If the word you pass is the last word you check for then your program ends up performing all of the checks in your function. This shouldn't be a problem in this case, but generally you don't want to flood your program with if statements, especially if you have a lot of cases.
Use a hashtable and just insert pairs. This way, all of your evaluateWord calls will return in amortized constant time. :)
Good luck!
Why do you need a (very subjective) "cleaner" way?
You could get more efficiency from using a hash lookup but you'd want to be certain it's called quite a bit to make the extra coding effort worthwhile. If it's something that happens infrequently (and, by that, I mean something like less than once a second), it's not worth doing (YAGNI).
One thing you might want to do for better looking code (if that's important) is to ditch the else bits, they're totally unnecessary:
private int evaluateWord(String sval) {
if (sval.equals("program")) return 1;
if (sval.equals("begin")) return 2;
if (sval.equals("end")) return 3;
if (sval.equals("int")) return 4;
if (sval.equals("if")) return 5;
System.exit(0);
}
You could just use an array or hashmap to map the enum values to the string values.
Inspired by your enum comment, I present the following. It's a bit hackish, but:
enum Word
{
PROGRAM (1), BEGIN (2), END (3), INT (4), IF (5);
public int value;
public Word (int value)
{
this.value = value;
}
};
int evaluateWord (String word)
{
return Word.valueOf(word.toUpperCase( )).value;
}
I love Java enums because you can do things like this. This is especially useful if you later want to (for example) add a unique behaviour for each word, or to maintain a long list of words. Note though that it is case insensitive.
Or, alternately:
enum Word
{
PROGRAM, BEGIN, END, INT, IF;
};
int evaluateWord (String word)
{
return Word.valueOf(word.toUpperCase( )).ordinal( ) + 1;
}