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Read methods from a text file and execute them in the program

I have a text file and that file lists all the operations that can be performed on a Pump Class.
example of the content of text file
Start PayCredit Reject Start PayCredit Reject TurnOff
....
.... so on.
These are the methods of the Pump class(Start(), Reject() etc)
I need to write a code where I can Read these method from the file one by one and execute them.
public static void main(String[] args) throws IOException
{
Pump gp= new Pump();
File file=new File("C:\\Users\\Desktop\\checker\\check.txt");
BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream(file)));
String line=null;
while((line=br.readLine())!=null)
{
String words[]=line.split(" ");
for(int i=0;i<words.length;i++)
{
String temp=words[i]+"()";
gp.temp; //compilation error
}
}
}
Could you tell me how can I achieve this functionality.

If you're not so familiar with reflection, maybe try using org.springframework.util.ReflectionUtils from the Spring Framework project?
The code would go something like this:
Pump gp = new Pump();
....
String temp = // from text file
....
Method m = ReflectionUtils.findMethod(Pump.class, temp);
Object result = ReflectionUtils.invokeMethod(m, gp);

You would need to use reflection to invoke the methods at runtime. Here is a simple example that assumes that all methods do not take any parameters.
Class<? extends Pump> pumpClass = gp.getClass();
String methodName = words[i];
Method toInvoke = pumpClass.getMethod(methodName);
if (null != toInvoke) {
toInvoke.invoke(gp);
}

First of all be aware that Java is not interpreted at runtime. So you can't do it this way.
If you already have the methods such as Start PayCredit Reject TurnOff and so on you can do it in the following way:
for(int i=0;i<words.length;i++)
{
String temp=words[i];
if (temp.equals("Start") gp.Start();
else if (temp.equals("PayCredit") gp.PayCredit();
...
}

use a switch case
for(int i=0;i<words.length;i++) {
String temp=words[i];
switch(temp) {
case "Start":
gp.start();
break;
case "PayCredit":
gp.PayCredit();
break;
}
}

You can use reflection to do this, e.g.
String line=null;
Method method = null;
while((line=br.readLine())!=null)
{
String words[]=line.split(" ");
for(int i=0;i<words.length;i++)
{
String temp=words[i];
method = getClass().getMethod(temp);
method.invoke(this);
}
}
That's assuming you want to call the method on this, of course, and that it's an instance method. Look at Class.getMethod and related methods, along with Method itself, for more details. You may want getDeclaredMethod instead, and you may need to make it accessible.
I would see if you can think of a way of avoiding this if possible though - reflection tends to get messy quickly. It's worth taking a step back and considering if this is the best design. If you give us more details of the bigger picture, we may be able to suggest alternatives.

Java writes writes line multiple times?

static void goOut(String in) {
//instance variables
String fileCopy = currentLine + in;
try {
FileWriter writer = new FileWriter(output,true);
writer.write(line1 + System.getProperty("line.separator", "\r\n"));
writer.write(fileCopy + System.getProperty("line.separator", "\r\n"));
} catch(IOException ex) {
ex.printStackTrace();
}
}
Edited code to the correct standard as pointed out by other users.

of course because thats what you r telling it to do. every time is called it writes both x and the number. a quick fix: you can keep a flag if it is the first run set it flag = true. and check within ur method, sth like this:
public class YourClass{
private boolean didRun = false;
static void goOut(String in) {
...... init ur file and writer
if(!didRun)
writer.write(Y);
writer.write(in);
writer.close();
didRun = true;
}
}
I dont know the rest of the code but i think thats what u need

I believe you want to separate the jobs the "goOut" is responsible for.
You should make "goOut" only write the numbers (in your example).
The writing of the y's (in your example) should not be apart of the method and called once, at the start of writing to the file.
Also, #Jon Skeet is right about the multiple FileWriters. Use one, since its the same file.

Agree, sounds like a disaster.
When you use multiple writers to access the file, I would expect to get unpredictable results.
I dont think there is any guarantee that FileWriter1 would complete the task before FileWriter2.
In addition, the method is not synchronized.

Getting an InputStream to read more than once, regardless of markSupported()

I need to be able to re-use a java.io.InputStream multiple times, and I figured the following code would work, but it only works the first time.
Code
public class Clazz
{
private java.io.InputStream dbInputStream, firstDBInputStream;
private ArrayTable db;
public Clazz(java.io.InputStream defDB)
{
this.firstDBInputStream = defDB;
this.dbInputStream = defDB;
if (db == null)
throw new java.io.FileNotFoundException("Could not find the database at " + db);
if (dbInputStream.markSupported())
dbInputStream.mark(Integer.MAX_VALUE);
loadDatabaseToArrayTable();
}
public final void loadDatabaseToArrayTable() throws java.io.IOException
{
this.dbInputStream = firstDBInputStream;
if (dbInputStream.markSupported())
dbInputStream.reset();
java.util.Scanner fileScanner = new java.util.Scanner(dbInputStream);
String CSV = "";
for (int i = 0; fileScanner.hasNextLine(); i++)
CSV += fileScanner.nextLine() + "\n";
db = ArrayTable.createArrayTableFromCSV(CSV);
}
public void reloadDatabase()//A method called by the UI
{
try
{
loadDatabaseToArrayTable();
}
catch (Throwable t)
{
//Alert the user that an error has occurred
}
}
}
Note that ArrayTable is a class of mine, which uses arrays to give an interface for working with tables.
Question
In this program, the database is shown directly to the user immediately after the reloadDatabase() method is called, and so any solution involving saving the initial read to an object in memory is useless, as that will NOT refresh the data (think of it like a browser; when you press "Refresh", you want it to fetch the information again, not just display the information it fetched the first time). How can I read a java.io.InputStream more than once?

You can't necessarily read an InputStream more than once. Some implementations support it, some don't. What you are doing is checking the markSupported method, which is indeed an indicator if you can read the same stream twice, but then you are ignoring the result. You have to call that method to see if you can read the stream twice, and if you can't, make other arrangements.
Edit (in response to comment): When I wrote my answer, my "other arrangements" was to get a fresh InputStream. However, when I read in your comments to your question about what you want to do, I'm not sure it is possible. For the basics of the operation, you probably want RandomAccessFile (at least that would be my first guess, and if it worked, that would be the easiest) - however you will have file access issues. You have an application actively writing to a file, and another reading that file, you will have problems - exactly which problems will depend on the OS, so whatever solution would require more testing. I suggest a separate question on SO that hits on that point, and someone who has tried that out can perhaps give you more insight.

you never mark the stream to be reset
public Clazz(java.io.InputStream defDB)
{
firstDBInputStream = defDB.markSupported()?defDB:new BufferedInputStream(defDB);
//BufferedInputStream supports marking
firstDBInputStream.mark(500000);//avoid IOException on first reset
}
public final void loadDatabaseToArrayTable() throws java.io.IOException
{
this.dbInputStream = firstDBInputStream;
dbInputStream.reset();
dbInputStream.mark(500000);//or however long the data is
java.util.Scanner fileScanner = new java.util.Scanner(dbInputStream);
StringBuilder CSV = "";//StringBuilder is more efficient in a loop
while(fileScanner.hasNextLine())
CSV.append(fileScanner.nextLine()).append("\n");
db = ArrayTable.createArrayTableFromCSV(CSV.toString());
}
however you could instead keep a copy of the original ArrayTable and copy that when you need to (or even the created string to rebuild it)
this code creates the string and caches it so you can safely discard the inputstreams and just use readCSV to build the ArrayTable
private String readCSV=null;
public final void loadDatabaseToArrayTable() throws java.io.IOException
{
if(readCSV==null){
this.dbInputStream = firstDBInputStream;
java.util.Scanner fileScanner = new java.util.Scanner(dbInputStream);
StringBuilder CSV = "";//StringBuilder is more efficient in a loop
while(fileScanner.hasNextLine())
CSV.append(fileScanner.nextLine()).append("\n");
readCSV=CSV.toString();
fileScanner.close();
}
db = ArrayTable.createArrayTableFromCSV(readCSV);
}
however if you want new information you'll need to create a new stream to read from again

Having trouble opening a file in Java

I am trying to open this file in java and i want to know what i am doing wrong. The in file lies in the same directory as my Java file, but i tried to open this with both netbeans and eclipse and it gave a file not found exception. Can someone help me open this file and read from it. I am really new to java files. Here is the code
import java.util.*;
import java.io.*;
public class Practice
{
public static void main(String[] args)throws IOException
{
FileReader fin = new FileReader("anagrams.in");
BufferedReader br = new BufferedReader(fin);
System.out.println(fin);
String string = "Madam Curie";
String test = "Radium came";
string = string.toLowerCase();
test = test.toLowerCase();
string = string.replaceAll("[^a-zA-Z0-9]+", "");
test = test.replaceAll("[^a-zA-Z0-9]+", "");
char[] array = string.toCharArray();
char[] array2 = test.toCharArray();
boolean flag = false;
HashMap hm = new HashMap();
for(int i = 0; i < array.length; i++)
{
hm.put(array[i], array[i]);
}
for(int i = 0; i < array2.length; i++)
{
if(hm.get(array2[i]) == null || test.length() != string.length())
{
flag = false;
i = array2.length;
}
else
{
flag = true;
}
}
System.out.println(flag);
}
}

A few tips:
Abide to proper code indentation
If you're using an IDE like Eclipse, it can automatically correct indentation for you
Develop debugging instinct
Try to get what the current working directory is, and list all the files in it
Refactor repetitive code
Writing paired statements like you did should immediately raise red flags
Effective Java 2nd Edition
Item 23: Don't use raw types in new code
Item 52: Refer to objects by their interfaces
Item 46: Prefer for-each loops to traditional for loops
Use sensible variable names
With regards to 2, try something like this:
public static void listDir() {
File current = new File(".");
System.out.println(current.getAbsolutePath());
for (String filename : current.list()) {
System.out.println(filename);
}
}
Then in your main, simply call listDir before everything else, and see if you're running the app from the right directory, and if there's a "anagrams.in" in the directory. Note that some platforms are case-sensitive.
With regards to 3 and 4, consider having a helper method like this:
static Set<Character> usedCharactersIn(String s) {
Set<Character> set = new HashSet<Character>();
for (char ch : s.toLowerCase().toCharArray()) {
set.add(ch);
}
return set;
}
Note how Set<E> is used instead of Map<K,V>. Looking at the rest of the code, you didn't seem to actually need a mapping, but rather a set of some sort (but more on that later).
You can then have something like this in main, which makes the logic very readable:
String s1 = ...;
String s2 = ...;
boolean isNotQuiteAnagram = (s1.length() == s2.length()) &&
usedCharactersIn(s1).containsAll(usedCharactersIn(s2));
Note how variables are now named rather sensibly, highlighting their roles. Note also that this logic does not quite determine that s1 is an anagram of s2 (consider e.g. "abb" and "aab"), but this is in fact what you were doing.
Since this looks like homework, I'll leave it up to you to try to figure out when two strings are anagrams.
See also
Java Coding Conventions
Java Language Guide/For-each loop
Java Tutorials/Collections Framework
Related questions
Why doesn't Java Map extends Collection?

Make sure that the file lies in the same directory as your .class file. It doesn't matter if it is in the same as your .java file or not.
Other than that, the only problem I can see is in your indentation, which doesn't matter.

The normal practice is to put resources in the runtime classpath or to add its path to the runtime classpath so that you can get it by the classloader. Using relative paths in Java IO is considered poor practice since it breaks portability. The relative path would be dependent on the current working directory over which you have totally no control from inside the Java code.
After having placed it in the classpath (assuming that it's in the same folder as the Java class itself), just do so:
BufferedReader reader = null;
try {
InputStream input = Practice.class.getResourceAsStream("anagrams.in");
reader = new BufferedReader(new InputStreamReader(input, "UTF-8")); // Or whatever encoding it is in.
// Process it.
// ...
} finally {
if (reader != null) try { reader.close(); } catch (IOException ignore) {}
}
Closing in finally is by the way mandatory to release the lock on the file after reading.

Put the anagrams.in file in the same location as the .class file. Then you will be able to read the file. And this should help you get some links on how to read from files in Java.

Is it possible to avoid temp files when a Java method expects Reader/Writer arguments?

I'm calling a method from an external library with a (simplified) signature like this:
public class Alien
{
// ...
public void munge(Reader in, Writer out) { ... }
}
The method basically reads a String from one stream and writes its results to the other. I have several strings which I need processed by this method, but none of them exist in the file system. The strings can get quite long (ca 300KB each). Ideally, I would like to call munge() as a filter:
public void myMethod (ArrayList<String> strings)
{
for (String s : strings) {
String result = alienObj.mungeString(s);
// do something with result
}
}
Unfortunately, the Alien class doesn't provide a mungeString() method, and wasn't designed to be inherited from. Is there a way I can avoid creating two temporary files every time I need to process a list of strings? Like, pipe my input to the Reader stream and read it back from the Writer stream, without actually touching the file system?
I'm new to Java, please forgive me if the answer is obvious to professionals.

You can easily avoid temporary files by using any/all of these:
CharArrayReader / CharArrayWriter
StringReader / StringWriter
PipedReader / PipedWriter
A sample mungeString() method could look like this:
public String mungeString(String input) {
StringWriter writer = new StringWriter();
alienObj.munge(new StringReader(input), writer));
return writer.toString();
}

StringReader
StringWriter

If you are welling to work with binary arrays in-memory like you do in C# then I think the PipedWriter & PipedReader are the most convenient way to do so. Check this:
Is it possible to avoid temp files when a Java method expects Reader/Writer arguments?