I am trying to implement the observer pattern to a game i have made. When a villain is created in the battle-zone file using threads, I would like to use the observer pattern to create a hero using threads and add it to the same file. The villians and heroes are created using the factory method pattern. I am unsure of where to go with regards to linking my HeroCreationMain class to the observer pattern classes.
Villian Creation
public class VillianCreationMain {
private static Villian villian;
public static void main(String[] args, int userInput) throws IOException {
String fileName = null;
Random randomVillian = new Random();
int amountOfVillians = userInput;
if (amountOfVillians < 7) {
for (int x = 0; x < amountOfVillians; x++) {
int randomGenerator = randomVillian.nextInt(6);
for (int i = 0; i < 5; i++) {
if (randomGenerator == 0 ) {
setVillian(new FlyingVillian());
}
else if (randomGenerator == 1) {
setVillian(new StrongVillian());
}
else if (randomGenerator == 2) {
setVillian(new FastVillian());
}
else if (randomGenerator == 3) {
setVillian(new SmartVillian());
}
else if (randomGenerator == 4) {
setVillian(new FireVillian());
}
else if (randomGenerator == 5) {
setVillian(new IceVillian());
}
try {
writeToFile(getVillian(), i, fileName);
}
catch (IOException e) {
System.out.println(e.getMessage());
}
}
VillianThreads t1 = new VillianThreads(VillianCreationMain.getVillian());
t1.start();
}
}
else {
System.out.println("Please enter a value of less than 7");
}
}
public static void writeToFile(Villian villian, int amountOfVillians, String fileName) throws IOException {
for(int x = 0; x < amountOfVillians; x++) {
// String parsedInt = Integer.toString(x);
fileName = "battle-zone.ser";
FileOutputStream file = new FileOutputStream(fileName);
ObjectOutputStream oos = new ObjectOutputStream(file);
oos.writeObject(villian);
file.close();
oos.close();
}
}
public static Villian getVillian() {
return villian;
}
public static void setVillian(Villian villian) {
VillianCreationMain.villian = villian;
}
}
Hero Creation
public class HeroCreationMain {
private static Hero hero = null;
public static void main(String[] Hero) {
EnemyStatus enemyStatus = new EnemyStatus();
VillianObserver observer1 = new VillianObserver(enemyStatus);
}
public static void readFile() throws IOException, ClassNotFoundException {
#SuppressWarnings("resource")
ObjectInputStream ois = new ObjectInputStream (new FileInputStream("battle-zone.ser"));
Villian targetVillian = (Villian) ois.readObject();
System.out.println(targetVillian + " is being attacked by a hero!");
}
public static Hero getHero() {
return hero;
}
public static void setHero(Hero hero) {
HeroCreationMain.hero = hero;
}
}
Observer
public interface Observer {
public void update(boolean enemyPresent);
}
public interface Subject {
public void register(Observer o);
public void unregister(Observer o);
public void notifyObserver();
}
Observable
public class VillianObserver implements Observer {
private boolean enemyPresent;
private static int heroIDTracker;
private int heroID;
private Subject villianObserver;
public VillianObserver(Subject villianObserver) {
this.villianObserver = villianObserver;
this.heroID = ++heroIDTracker;
System.out.println("New Observer " + this.heroID);
villianObserver.register(this);
}
#Override
public void update(boolean enemyPresent) {
this.enemyPresent = enemyPresent;
printResult();
}
public void printResult() {
System.out.println(heroID + " " + enemyPresent);
}
}
Enemy Status
import java.util.ArrayList;
public class EnemyStatus implements Subject {
private ArrayList<Observer> observers;
private boolean enemyPresent;
public EnemyStatus() {
// Creates an ArrayList to hold all observers
observers = new ArrayList<Observer>();
}
#Override
public void register(Observer newObserver) {
observers.add(newObserver);
}
#Override
public void unregister(Observer deleteObserver) {
// Get the index of the observer to delete
int heroIndex = observers.indexOf(deleteObserver);
// Print out message (Have to increment index to match
System.out.println("Observer " + (heroIndex+1) + " deleted");
// Removes observer from the ArrayList
observers.remove(heroIndex);
}
#Override
public void notifyObserver() {
for(Observer observer : observers) {
observer.update(enemyPresent);
}
}
public void setEnemyStatus(boolean enemyPresent) {
this.enemyPresent = enemyPresent;
notifyObserver();
}
}
JNotify is the Java library to observe file changes on the file system.
One piece of advice: Object(Input/Output)Streams are easy when you're just getting started but they lead you down a path of ruin. Objects get so easily BadVersion'ed. Object files are also relatively hard to inspect using a text editor. I'd advise you to try using a different data format (like JSON) instead.
I try to create a Class in Processing,
it includes 3 bool´s, and I want to make a getter, setter, resp. a method which changes the boolean to the other value.
That´s it.
My Code is following:
public class Color_high_low {
private boolean r_higher = true;
private boolean g_higher = true;
private boolean b_higher = true;
Color_high_low() {
r_higher = true;
g_higher = true;
b_higher = true;
}
//Getter
{
boolean get_r_h() {
return r_higher;
}
boolean get_g_h() {
return this.r_higher;
}
boolean get_b_h() {
return this.r_higher;
}
}
//Changer
{
void change_r_h() {
if (r_higher == true) {
r_higher = false;
} else {
r_higher = true;
}
return;
}
void change_g_h() {
if (g_higher == true) {
g_higher = false;
} else {
g_higher = true;
}
return;
}
void change_b_h() {
if (b_higher == true) {
b_higher = false;
} else {
b_higher = true;
}
return;
}
}
//Setter
{
void set_r_h(boolean be_or_not_to_be) {
r_higher = be_or_not_to_be;
return;
}
void set_g_h(boolean be_or_not_to_be) {
g_higher = be_or_not_to_be;
return;
}
void set_b_h(boolean be_or_not_to_be) {
b_higher = be_or_not_to_be;
return;
}
}
}
At the moment I get compile errors by the Return-Types of my methods, but I don´t know why. Do you have ideas?
Answers would be a pleasure!
Compile errors at the moment:
unexpected token: boolean
unexpected token: void
Don´t put methods in extra backets {} for grouping!
Hello I'm new in programming, and sorry for my English.
So question is, for example: we have string "cabbaa"
and I should get 1c1a2b2a
which means: 1 times'c', 1 times'a', 2 times'b', 2 times'a'
I could write code which gets 1c3a2b:
public class test {
static int i,j,k,c=0,w;
static char m;
public static void main(String[] args) {
frequencycount("cabbaa");
}
static void frequencycount(String s)
{
char[] z=new char[s.length()];
for(w=0;w<s.length();w++)
z[w]=s.charAt(w);
for(i=0;i<w;i++)
{
char ch=z[i];
for(j=i+1;j<w;j++)
{
if(z[j]==ch)
{
for(k=j;k<(w-1);k++)
z[k]=z[k+1];
w--;
j=i;
}
}
}
int[] t=new int[w];
for(i=0;i<w;i++)
{
for(j=0,c=0;j<s.length();j++)
{
if(z[i]==s.charAt(j))
c++;
}
t[i]=c ;
System.out.print(c+""+z[i]);
}
}
}
in this code I guess I compared all characters overall from string and got 1c3a2b, but I should get 1c1a2b2a.
Any help appreciated.
This should do the job:
public class test {
public static void main(String[] args) {
frequencycount("cabbaa");
}
static void frequencycount(String s) {
StringBuilder output = new StringBuilder();
Character previousCharacter = null;
int counter = -1;
for (Character c : s.toCharArray()) {
if (c.equals(previousCharacter)) {
counter++;
} else {
if (previousCharacter != null) {
output.append(counter);
output.append(previousCharacter);
}
counter = 1;
previousCharacter = c;
}
}
if (previousCharacter != null) {
output.append(counter);
output.append(previousCharacter);
}
System.out.println("Res: " + output);
}
}
I am reading this page about coroutines in Python and this Wikipedia page. I saw that there are a few libraries in Java implementing coroutines.
My question is: is there any known reason why the Java designers decided not to implement coroutines so far and is there any plan to include it in a future version of Java?
Thanks.
Actually the concept of a co-routine was the first design of the Java threading system. The wait/notify mechanism is a simplistic form of co-routine where notify is equivalent to yield etc.
Since then much has been done, particularly to make structures thread-safe rather than algorithms. This derives from the realization that it is not the code that must synchronize/yield but the data structure used to communicate between the threads that must be thread-safe.
Project Loom
Continuations and Coroutines will come to Java in the nearer future and they’ll be called virtual threads (also referred to as fibers). There’s a project called Loom:
Project Loom is intended to explore, incubate and deliver Java VM features and APIs built on top of them for the purpose of supporting easy-to-use, high-throughput lightweight concurrency and new programming models on the Java platform. This is accomplished by the addition of the following constructs:
Virtual threads
Delimited continuations
Tail-call elimination
Further reading: https://cr.openjdk.java.net/~rpressler/loom/Loom-Proposal.html
To quote that document:
It is the goal of this project to add a public delimited continuation (or coroutine) construct to the Java platform. However, this goal is secondary to fibers …
Preliminary builds of Project Loom are available now, based on early-access Java 16.
On the "are there any plans ..." part of the question, the answer is:
Not at this stage
The JEP list (http://openjdk.java.net/jeps/0) does not make any mention of coroutines. The list covers features added in Java 8, added or targeted for Java 9, or proposed for future releases.
Interestingly, there was an RFE submitted in March 2013 (https://bugs.openjdk.java.net/browse/JDK-8029988). The RFE only got one vote, and it was closed 9 months with the suggestion to submit a JEP. Nobody has bothered to take the idea any further, which to me is telling.
It's synced with Java 15 build 7.
Link
There's an another choice is here for Java6+
A pythonic coroutine implementation:
import java.lang.ref.WeakReference;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.*;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicReference;
class CorRunRAII {
private final List<WeakReference<? extends CorRun>> resources = new ArrayList<>();
public CorRunRAII add(CorRun resource) {
if (resource == null) {
return this;
}
resources.add(new WeakReference<>(resource));
return this;
}
public CorRunRAII addAll(List<? extends CorRun> arrayList) {
if (arrayList == null) {
return this;
}
for (CorRun corRun : arrayList) {
add(corRun);
}
return this;
}
#Override
protected void finalize() throws Throwable {
super.finalize();
for (WeakReference<? extends CorRun> corRunWeakReference : resources) {
CorRun corRun = corRunWeakReference.get();
if (corRun != null) {
corRun.stop();
}
}
}
}
class CorRunYieldReturn<ReceiveType, YieldReturnType> {
public final AtomicReference<ReceiveType> receiveValue;
public final LinkedBlockingDeque<AtomicReference<YieldReturnType>> yieldReturnValue;
CorRunYieldReturn(AtomicReference<ReceiveType> receiveValue, LinkedBlockingDeque<AtomicReference<YieldReturnType>> yieldReturnValue) {
this.receiveValue = receiveValue;
this.yieldReturnValue = yieldReturnValue;
}
}
interface CorRun<ReceiveType, YieldReturnType> extends Runnable, Callable<YieldReturnType> {
boolean start();
void stop();
void stop(final Throwable throwable);
boolean isStarted();
boolean isEnded();
Throwable getError();
ReceiveType getReceiveValue();
void setResultForOuter(YieldReturnType resultForOuter);
YieldReturnType getResultForOuter();
YieldReturnType receive(ReceiveType value);
ReceiveType yield();
ReceiveType yield(YieldReturnType value);
<TargetReceiveType, TargetYieldReturnType> TargetYieldReturnType yieldFrom(final CorRun<TargetReceiveType, TargetYieldReturnType> another);
<TargetReceiveType, TargetYieldReturnType> TargetYieldReturnType yieldFrom(final CorRun<TargetReceiveType, TargetYieldReturnType> another, final TargetReceiveType value);
}
abstract class CorRunSync<ReceiveType, YieldReturnType> implements CorRun<ReceiveType, YieldReturnType> {
private ReceiveType receiveValue;
public final List<WeakReference<CorRun>> potentialChildrenCoroutineList = new ArrayList<>();
// Outside
private AtomicBoolean isStarted = new AtomicBoolean(false);
private AtomicBoolean isEnded = new AtomicBoolean(false);
private Throwable error;
private YieldReturnType resultForOuter;
#Override
public boolean start() {
boolean isStarted = this.isStarted.getAndSet(true);
if ((! isStarted)
&& (! isEnded())) {
receive(null);
}
return isStarted;
}
#Override
public void stop() {
stop(null);
}
#Override
public void stop(Throwable throwable) {
isEnded.set(true);
if (throwable != null) {
error = throwable;
}
for (WeakReference<CorRun> weakReference : potentialChildrenCoroutineList) {
CorRun child = weakReference.get();
if (child != null) {
child.stop();
}
}
}
#Override
public boolean isStarted() {
return isStarted.get();
}
#Override
public boolean isEnded() {
return isEnded.get();
}
#Override
public Throwable getError() {
return error;
}
#Override
public ReceiveType getReceiveValue() {
return receiveValue;
}
#Override
public void setResultForOuter(YieldReturnType resultForOuter) {
this.resultForOuter = resultForOuter;
}
#Override
public YieldReturnType getResultForOuter() {
return resultForOuter;
}
#Override
public synchronized YieldReturnType receive(ReceiveType value) {
receiveValue = value;
run();
return getResultForOuter();
}
#Override
public ReceiveType yield() {
return yield(null);
}
#Override
public ReceiveType yield(YieldReturnType value) {
resultForOuter = value;
return receiveValue;
}
#Override
public <TargetReceiveType, TargetYieldReturnType> TargetYieldReturnType yieldFrom(CorRun<TargetReceiveType, TargetYieldReturnType> another) {
return yieldFrom(another, null);
}
#Override
public <TargetReceiveType, TargetYieldReturnType> TargetYieldReturnType yieldFrom(CorRun<TargetReceiveType, TargetYieldReturnType> another, TargetReceiveType value) {
if (another == null || another.isEnded()) {
throw new RuntimeException("Call null or isEnded coroutine");
}
potentialChildrenCoroutineList.add(new WeakReference<CorRun>(another));
synchronized (another) {
boolean isStarted = another.start();
boolean isJustStarting = ! isStarted;
if (isJustStarting && another instanceof CorRunSync) {
return another.getResultForOuter();
}
return another.receive(value);
}
}
#Override
public void run() {
try {
this.call();
}
catch (Exception e) {
e.printStackTrace();
stop(e);
return;
}
}
}
abstract class CorRunThread<ReceiveType, YieldReturnType> implements CorRun<ReceiveType, YieldReturnType> {
private final ExecutorService childExecutorService = newExecutorService();
private ExecutorService executingOnExecutorService;
private static final CorRunYieldReturn DUMMY_COR_RUN_YIELD_RETURN = new CorRunYieldReturn(new AtomicReference<>(null), new LinkedBlockingDeque<AtomicReference>());
private final CorRun<ReceiveType, YieldReturnType> self;
public final List<WeakReference<CorRun>> potentialChildrenCoroutineList;
private CorRunYieldReturn<ReceiveType, YieldReturnType> lastCorRunYieldReturn;
private final LinkedBlockingDeque<CorRunYieldReturn<ReceiveType, YieldReturnType>> receiveQueue;
// Outside
private AtomicBoolean isStarted = new AtomicBoolean(false);
private AtomicBoolean isEnded = new AtomicBoolean(false);
private Future<YieldReturnType> future;
private Throwable error;
private final AtomicReference<YieldReturnType> resultForOuter = new AtomicReference<>();
CorRunThread() {
executingOnExecutorService = childExecutorService;
receiveQueue = new LinkedBlockingDeque<>();
potentialChildrenCoroutineList = new ArrayList<>();
self = this;
}
#Override
public void run() {
try {
self.call();
}
catch (Exception e) {
stop(e);
return;
}
stop();
}
#Override
public abstract YieldReturnType call();
#Override
public boolean start() {
return start(childExecutorService);
}
protected boolean start(ExecutorService executorService) {
boolean isStarted = this.isStarted.getAndSet(true);
if (!isStarted) {
executingOnExecutorService = executorService;
future = (Future<YieldReturnType>) executingOnExecutorService.submit((Runnable) self);
}
return isStarted;
}
#Override
public void stop() {
stop(null);
}
#Override
public void stop(final Throwable throwable) {
if (throwable != null) {
error = throwable;
}
isEnded.set(true);
returnYieldValue(null);
// Do this for making sure the coroutine has checked isEnd() after getting a dummy value
receiveQueue.offer(DUMMY_COR_RUN_YIELD_RETURN);
for (WeakReference<CorRun> weakReference : potentialChildrenCoroutineList) {
CorRun child = weakReference.get();
if (child != null) {
if (child instanceof CorRunThread) {
((CorRunThread)child).tryStop(childExecutorService);
}
}
}
childExecutorService.shutdownNow();
}
protected void tryStop(ExecutorService executorService) {
if (this.executingOnExecutorService == executorService) {
stop();
}
}
#Override
public boolean isEnded() {
return isEnded.get() || (
future != null && (future.isCancelled() || future.isDone())
);
}
#Override
public boolean isStarted() {
return isStarted.get();
}
public Future<YieldReturnType> getFuture() {
return future;
}
#Override
public Throwable getError() {
return error;
}
#Override
public void setResultForOuter(YieldReturnType resultForOuter) {
this.resultForOuter.set(resultForOuter);
}
#Override
public YieldReturnType getResultForOuter() {
return this.resultForOuter.get();
}
#Override
public YieldReturnType receive(ReceiveType value) {
LinkedBlockingDeque<AtomicReference<YieldReturnType>> yieldReturnValue = new LinkedBlockingDeque<>();
offerReceiveValue(value, yieldReturnValue);
try {
AtomicReference<YieldReturnType> takeValue = yieldReturnValue.take();
return takeValue == null ? null : takeValue.get();
} catch (InterruptedException e) {
e.printStackTrace();
}
return null;
}
#Override
public ReceiveType yield() {
return yield(null);
}
#Override
public ReceiveType yield(final YieldReturnType value) {
returnYieldValue(value);
return getReceiveValue();
}
#Override
public <TargetReceiveType, TargetYieldReturnType> TargetYieldReturnType yieldFrom(final CorRun<TargetReceiveType, TargetYieldReturnType> another) {
return yieldFrom(another, null);
}
#Override
public <TargetReceiveType, TargetYieldReturnType> TargetYieldReturnType yieldFrom(final CorRun<TargetReceiveType, TargetYieldReturnType> another, final TargetReceiveType value) {
if (another == null || another.isEnded()) {
throw new RuntimeException("Call null or isEnded coroutine");
}
boolean isStarted = false;
potentialChildrenCoroutineList.add(new WeakReference<CorRun>(another));
synchronized (another) {
if (another instanceof CorRunThread) {
isStarted = ((CorRunThread)another).start(childExecutorService);
}
else {
isStarted = another.start();
}
boolean isJustStarting = ! isStarted;
if (isJustStarting && another instanceof CorRunSync) {
return another.getResultForOuter();
}
TargetYieldReturnType send = another.receive(value);
return send;
}
}
#Override
public ReceiveType getReceiveValue() {
setLastCorRunYieldReturn(takeLastCorRunYieldReturn());
return lastCorRunYieldReturn.receiveValue.get();
}
protected void returnYieldValue(final YieldReturnType value) {
CorRunYieldReturn<ReceiveType, YieldReturnType> corRunYieldReturn = lastCorRunYieldReturn;
if (corRunYieldReturn != null) {
corRunYieldReturn.yieldReturnValue.offer(new AtomicReference<>(value));
}
}
protected void offerReceiveValue(final ReceiveType value, LinkedBlockingDeque<AtomicReference<YieldReturnType>> yieldReturnValue) {
receiveQueue.offer(new CorRunYieldReturn(new AtomicReference<>(value), yieldReturnValue));
}
protected CorRunYieldReturn<ReceiveType, YieldReturnType> takeLastCorRunYieldReturn() {
try {
return receiveQueue.take();
} catch (InterruptedException e) {
e.printStackTrace();
}
return null;
}
protected void setLastCorRunYieldReturn(CorRunYieldReturn<ReceiveType,YieldReturnType> lastCorRunYieldReturn) {
this.lastCorRunYieldReturn = lastCorRunYieldReturn;
}
protected ExecutorService newExecutorService() {
return Executors.newCachedThreadPool(getThreadFactory());
}
protected ThreadFactory getThreadFactory() {
return new ThreadFactory() {
#Override
public Thread newThread(final Runnable runnable) {
Thread thread = new Thread(runnable);
thread.setUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler() {
#Override
public void uncaughtException(Thread thread, Throwable throwable) {
throwable.printStackTrace();
if (runnable instanceof CorRun) {
CorRun self = (CorRun) runnable;
self.stop(throwable);
thread.interrupt();
}
}
});
return thread;
}
};
}
}
Now you can use pythonic coroutines in this way
(e.g. fibonacci numbers)
Thread Version:
class Fib extends CorRunThread<Integer, Integer> {
#Override
public Integer call() {
Integer times = getReceiveValue();
do {
int a = 1, b = 1;
for (int i = 0; times != null && i < times; i++) {
int temp = a + b;
a = b;
b = temp;
}
// A pythonic "yield", i.e., it returns `a` to the caller and waits `times` value from the next caller
times = yield(a);
} while (! isEnded());
setResultForOuter(Integer.MAX_VALUE);
return getResultForOuter();
}
}
class MainRun extends CorRunThread<String, String> {
#Override
public String call() {
// The fib coroutine would be recycled by its parent
// (no requirement to call its start() and stop() manually)
// Otherwise, if you want to share its instance and start/stop it manually,
// please start it before being called by yieldFrom() and stop it in the end.
Fib fib = new Fib();
String result = "";
Integer current;
int times = 10;
for (int i = 0; i < times; i++) {
// A pythonic "yield from", i.e., it calls fib with `i` parameter and waits for returned value as `current`
current = yieldFrom(fib, i);
if (fib.getError() != null) {
throw new RuntimeException(fib.getError());
}
if (current == null) {
continue;
}
if (i > 0) {
result += ",";
}
result += current;
}
setResultForOuter(result);
return result;
}
}
Sync(non-thread) version:
class Fib extends CorRunSync<Integer, Integer> {
#Override
public Integer call() {
Integer times = getReceiveValue();
int a = 1, b = 1;
for (int i = 0; times != null && i < times; i++) {
int temp = a + b;
a = b;
b = temp;
}
yield(a);
return getResultForOuter();
}
}
class MainRun extends CorRunSync<String, String> {
#Override
public String call() {
CorRun<Integer, Integer> fib = null;
try {
fib = new Fib();
} catch (Exception e) {
e.printStackTrace();
}
String result = "";
Integer current;
int times = 10;
for (int i = 0; i < times; i++) {
current = yieldFrom(fib, i);
if (fib.getError() != null) {
throw new RuntimeException(fib.getError());
}
if (current == null) {
continue;
}
if (i > 0) {
result += ",";
}
result += current;
}
stop();
setResultForOuter(result);
if (Utils.isEmpty(result)) {
throw new RuntimeException("Error");
}
return result;
}
}
Execution(Both versions will work):
// Run the entry coroutine
MainRun mainRun = new MainRun();
mainRun.start();
// Wait for mainRun ending for 5 seconds
long startTimestamp = System.currentTimeMillis();
while(!mainRun.isEnded()) {
if (System.currentTimeMillis() - startTimestamp > TimeUnit.SECONDS.toMillis(5)) {
throw new RuntimeException("Wait too much time");
}
}
// The result should be "1,1,2,3,5,8,13,21,34,55"
System.out.println(mainRun.getResultForOuter());
I have implemented the algorithm that I have found on this link to evaluate an arithmetic expression for j2me. But it works fine only when I have single digit operands i.e. 2, 5, 7, 3 but not for 456, 56, 34.45 etc. I did some changes as i knew i had to add the numbers found not one by one but till we end with a digit. Then I found this link also but still things didn't go well as expected. First I had tried the exp4j library but I guess that does not work on j2me. The code has become very messy right now. Could I get any opinions on how should I go about this problem? Any help on this would be appreciated.
Code that initially worked only for single digit operands:
import java.util.Stack;
import java.util.Vector;
import java.util.logging.Level;
import java.util.logging.Logger;
public class SampleInfixToPostfixToResult {
static Stack stack=new Stack();
static StringBuffer p=new StringBuffer();
static Vector v=new Vector();
public static StringBuffer toPostfix(String q)
{
for(int i=0;i<q.length();i++)
{
if(q.charAt(i)=='0'||q.charAt(i)=='1'||q.charAt(i)=='2'||q.charAt(i)=='3'||q.charAt(i)=='4'||q.charAt(i)=='5'||q.charAt(i)=='6'||q.charAt(i)=='7'||q.charAt(i)=='8'||q.charAt(i)=='9')
{
p.append(q.charAt(i));
}
else if(q.charAt(i)=='(')
{
stack.push(q.charAt(i));
}
else if(q.charAt(i)==')')
{
for(int j=0;!stack.empty()&&!stack.peek().equals('(');j++)
{
p.append(stack.pop());
}
stack.pop();
}
else if(q.charAt(i)=='+'||q.charAt(i)=='-'||q.charAt(i)=='/'||q.charAt(i)=='*')
{
if(stack.empty()||stack.peek().equals('('))
stack.push(q.charAt(i));
else
{
while(!stack.empty()&&!stack.peek().equals('(')&&isHigh(q.charAt(i), stack.peek()))
{
p.append(stack.pop());
}
stack.push(q.charAt(i));
}
}
}
while(!stack.empty())
{
p.append(stack.pop());
}
System.out.println(p);
return p;
}
public static boolean isHigh(char op, Object AtStack)
{
char opAtStack=AtStack.toString().charAt(0);
boolean isHigh=false;
if((op==opAtStack))
isHigh=true;
if((op=='+'||op=='-')&&(opAtStack=='/'||opAtStack=='*'))
{
isHigh=true;
}
if((op=='+'&&opAtStack=='-')||(op=='-'&&opAtStack=='+')||(op=='/'&&opAtStack=='*')||(op=='*'&&opAtStack=='/'))
{
isHigh=true;
}
return isHigh;
}
public static double result(StringBuffer p)
{
for(int i=0;i<p.length();i++)
{
System.out.println(p.charAt(i));
if(p.charAt(i)=='0'||p.charAt(i)=='1'||p.charAt(i)=='2'||p.charAt(i)=='3'||p.charAt(i)=='4'||p.charAt(i)=='5'||p.charAt(i)=='6'||p.charAt(i)=='7'||p.charAt(i)=='8'||p.charAt(i)=='9')
{
stack.push(p.charAt(i));
}
if(p.charAt(i)=='+'||p.charAt(i)=='-'||p.charAt(i)=='/'||p.charAt(i)=='*')
{
double a=Double.parseDouble(stack.pop().toString());
double b=Double.parseDouble(stack.pop().toString());
if(p.charAt(i)=='+')
{
stack.push(b+a);
}
else if(p.charAt(i)=='-')
{
stack.push(b-a);
}
else if(p.charAt(i)=='/')
{
stack.push(b/a);
}
else if(p.charAt(i)=='*')
{
stack.push(b*a);
}
}
}
System.out.println(stack);
return 0;
}
public static void main(String[] args) {
// TODO code application logic here
String s=new String("65*(76+2)-0/4+(2*5-6*(2*5))");
SampleInfixToPostfixToResult.result(SampleInfixToPostfixToResult.toPostfix(s));
System.out.println(66*(76+2)-0/4+(2*5-6*(2*5)));
}
}
Updated code that I worked on for evaluation of multi-digit operand (really messed up)
import java.util.Stack;
import java.util.Vector;
import java.util.logging.Level;
import java.util.logging.Logger;
public class SampleInfixToPostfixToResult {
static Stack stack=new Stack();
static StringBuffer p=new StringBuffer();
static Vector v=new Vector();
public static Vector toPostfix(String q)
{
for(int i=0;i<q.length();i++)
{
if(q.charAt(i)=='0'||q.charAt(i)=='1'||q.charAt(i)=='2'||q.charAt(i)=='3'||q.charAt(i)=='4'||q.charAt(i)=='5'||q.charAt(i)=='6'||q.charAt(i)=='7'||q.charAt(i)=='8'||q.charAt(i)=='9')
{
StringBuffer tn=new StringBuffer();
while(i<q.length()&&(q.charAt(i)=='0'||q.charAt(i)=='1'||q.charAt(i)=='2'||q.charAt(i)=='3'||q.charAt(i)=='4'||q.charAt(i)=='5'||q.charAt(i)=='6'||q.charAt(i)=='7'||q.charAt(i)=='8'||q.charAt(i)=='9'))
{
tn.append(q.charAt(i++));
}
v.add(tn);
}
else if(q.charAt(i)=='(')
{
stack.push(q.charAt(i));
}
else if(q.charAt(i)==')')
{
for(int j=0;!stack.empty()&&!stack.peek().equals('(');j++)
{
v.add(stack.pop());
}
stack.pop();
}
else if(q.charAt(i)=='+'||q.charAt(i)=='-'||q.charAt(i)=='/'||q.charAt(i)=='*')
{
if(stack.empty()||stack.peek().equals('('))
stack.push(q.charAt(i));
else
{
while(!stack.empty()&&!stack.peek().equals('(')&&isHigh(q.charAt(i), stack.peek()))
{
v.add(stack.pop());
}
stack.push(q.charAt(i));
}
}
}
while(!stack.empty())
{
v.add(stack.pop());
}
return v;
}
public static boolean isHigh(char op, Object AtStack)
{
char opAtStack=AtStack.toString().charAt(0);
boolean isHigh=false;
if((op==opAtStack))
isHigh=true;
if((op=='+'||op=='-')&&(opAtStack=='/'||opAtStack=='*'))
{
isHigh=true;
}
if((op=='+'&&opAtStack=='-')||(op=='-'&&opAtStack=='+')||(op=='/'&&opAtStack=='*')||(op=='*'&&opAtStack=='/'))
{
isHigh=true;
}
return isHigh;
}
public static double result(Vector p)
{
for(int i=0;i<p.size();i++)
{
System.out.println(p.get(i));
if(p.get(i)=="0"||p.get(i)=="1"||p.get(i)=="2"||p.get(i)=="3"||p.get(i)=="4"||p.get(i)=="5"||p.get(i)=="6"||p.get(i)=="7"||p.get(i)=="8"||p.get(i)=="9")
{
StringBuffer tn=new StringBuffer();
while(i<p.size()&&(p.get(i)=="0"||p.get(i)=="1"||p.get(i)=="2"||p.get(i)=="3"||p.get(i)=="4"||p.get(i)=="5"||p.get(i)=="6"||p.get(i)=="7"||p.get(i)=="8"||p.get(i)=="9"))
{
tn.append(p.get(i++));
}
System.out.println("This is the full number :"+tn);
stack.push(tn);
}
if(p.get(i)=="+"||p.get(i)=="-"||p.get(i)=="/"||p.get(i)=="*")
{
double a=Double.parseDouble(stack.pop().toString());
double b=Double.parseDouble(stack.pop().toString());
if(p.get(i)=="+")
{
stack.push(b+a);
}
else if(p.get(i)=="-")
{
stack.push(b-a);
}
else if(p.get(i)=="/")
{
stack.push(b/a);
}
else if(p.get(i)=="*")
{
stack.push(b*a);
}
}
}
System.out.println("Final value: "+stack);
return 0;
}
public static void main(String[] args) {
// TODO code application logic here
String s=new String("65*(79+22)-0/4+(29*5-6*(2*5))");
SampleInfixToPostfixToResult.result(SampleInfixToPostfixToResult.toPostfix(s));
//System.out.println(65*(79+22)-0/4+(29*5-6*(2*5)));
}
}
Solution:
1.Function toPostfix() now returns stack instead of vector, as now the postfix expression is added to the stack eg, [34,57.+] etc.
2.Edited the code for storing all the digits to the stack by traversing the string till we have a number.(see code till line no 29)
import java.util.Stack;
import java.util.Vector;
/*
* To change this template, choose Tools | Templates
* and open the template in the editor.
*/
/**
*
* #author Sandeep
*/
public class Main {
static Stack stack=new Stack();
static Stack stackT=new Stack();
//static Vector v=new Vector();
//static StringBuffer p=new StringBuffer();
public static Stack toPostfix(String q)
{
for(int i=0;i<q.length();i++)
{
if(q.charAt(i)=='0'||q.charAt(i)=='1'||q.charAt(i)=='2'||q.charAt(i)=='3'||q.charAt(i)=='4'||q.charAt(i)=='5'||q.charAt(i)=='6'||q.charAt(i)=='7'||q.charAt(i)=='8'||q.charAt(i)=='9')
{
StringBuffer p=new StringBuffer();
while(q.charAt(i)=='0'||q.charAt(i)=='1'||q.charAt(i)=='2'||q.charAt(i)=='3'||q.charAt(i)=='4'||q.charAt(i)=='5'||q.charAt(i)=='6'||q.charAt(i)=='7'||q.charAt(i)=='8'||q.charAt(i)=='9')
p.append(q.charAt(i++));
stackT.push(p);
i--;
}
else if(q.charAt(i)=='(')
{
stack.push(q.charAt(i));
}
else if(q.charAt(i)==')')
{
for(int j=0;!stack.empty()&&!stack.peek().equals('(');j++)
{
stackT.push(stack.pop().toString());
}
stack.pop();
}
else if(q.charAt(i)=='+'||q.charAt(i)=='-'||q.charAt(i)=='/'||q.charAt(i)=='*')
{
if(stack.empty()||stack.peek().equals('('))
stack.push(q.charAt(i));
else
{
while(!stack.empty()&&!stack.peek().equals('(')&&isHigh(q.charAt(i), stack.peek()))
{
stackT.push(stack.pop().toString());
}
stack.push(q.charAt(i));
}
}
}
while(!stack.empty())
{
stackT.push(stack.pop().toString());
}
System.out.println(stackT);
return stackT;
}
//problem lies here
public static boolean isHigh(char op, Object AtStack)
{
char opAtStack=AtStack.toString().charAt(0);
boolean isHigh=false;
if((op==opAtStack))
isHigh=true;
if((op=='+'||op=='-')&&(opAtStack=='/'||opAtStack=='*'))
{
isHigh=true;
}
if((op=='+'&&opAtStack=='-')||(op=='-'&&opAtStack=='+')||(op=='/'&&opAtStack=='*')||(op=='*'&&opAtStack=='/'))
{
isHigh=true;
}
return isHigh;
}
public static double result(Stack p)
{
for(int i=0;i<p.size();i++)
{
if(p.get(i).toString().startsWith("0")||p.get(i).toString().startsWith("1")||p.get(i).toString().startsWith("2")||p.get(i).toString().startsWith("3")||p.get(i).toString().startsWith("4")||p.get(i).toString().startsWith("5")||p.get(i).toString().startsWith("6")||p.get(i).toString().startsWith("7")||p.get(i).toString().startsWith("8")||p.get(i).toString().startsWith("9"))
{
stack.push(p.get(i));
}
if(p.get(i).toString().equals("+")||p.get(i).toString().equals("-")||p.get(i).toString().equals("/")||p.get(i).toString().equals("*"))
{
double a=Double.parseDouble(stack.pop().toString());
double b=Double.parseDouble(stack.pop().toString());
if(p.get(i).equals("+"))
{
stack.push(b+a);
}
else if(p.get(i).equals("-"))
{
stack.push(b-a);
}
else if(p.get(i).equals("/"))
{
stack.push(b/a);
}
else if(p.get(i).equals("*"))
{
stack.push(b*a);
}
}
}
System.out.println(stack);
return 0;
}
public static void main(String[] args) {
// TODO code application logic here
String s=new String("159*(79+23)-10/4+(22*54-67*(25*58))");
Main.result(Main.toPostfix(s));
System.out.println(159*(79+23)-10/4+(22*54-67*(25*58)));
}
}