sorry, changed the question slightly.
essentially i want to know if aString contains String. My issue is when comparing say aS a substring of aString) "aS".contains("String") shows true.
String a="st", b="string";
I ran System.out.println(a.contains(b));
That returned false, as expected. I have an understanding of contains, i must be missing something else.
So It had seemed that my program was working properly, but I made some adjustments and came back and the whole thing stopped working. I sussed out what are usually the common culprits (brackets, file io, etc.). I found if(string.contains(string)) would continually run, ie: always true. not sure why this is happening, probably something I missed in the code.
This is an example of my output (Just a char by char reading of the file):
I
n
t
e
g
e
r
G
;
import java.io.File;
import java.util.ArrayList;
import java.util.Scanner;
public class comp{
public static void main(String[] args){
ArrayList<String> lines = new ArrayList<String>();
ArrayList<String> symbolTable = new ArrayList<String>();
ArrayList<String> parsedFile = new ArrayList<String>();
try {
File file = new File("symbolTable.txt");
Scanner scanner=new Scanner(file);
while (scanner.hasNextLine()&&symbolTable.add(scanner.nextLine().replaceAll("\\s+","").toLowerCase()));
scanner.close();
} catch (Exception ex) {
ex.printStackTrace();
}
try {
File file = new File("APU_CS400_input.txt");
Scanner scanner=new Scanner(file);
while (scanner.hasNextLine()&&lines.add(scanner.nextLine().replaceAll("\\s+","").toLowerCase()));
scanner.close();
} catch (Exception ex) {
ex.printStackTrace();
}
//runs through line by line of the input file
for(String line: lines){
String sBuild = "";
StringBuilder identifier = new StringBuilder("");
//moves through the line char by char
for(int i=0;line.length()>i; i++){
sBuild+=line.charAt(i);
//moves through the symbol table comparing each symbol to each string
//that is built char by char
for(String symbol: symbolTable){
//if the char string matches the symbol then any identifiers are saved and
//symbols are saved, the string is then reset to empty
//This is where i seem to get an issue
***if(sBuild.contains(symbol)){***
if(symbol.length()<sBuild.length()){
identifier.append(sBuild,0,sBuild.length()-symbol.length());
parsedFile.add(identifier.toString());
identifier.delete(0,sBuild.length()-symbol.length());
}
sBuild="";
parsedFile.add(symbol);
}
}
}
}
for(String symbol:parsedFile){
System.out.println(symbol);
}
}
}
Blockquote
Think of it this way.
s1.contains(s2)
should return true, if a substring of s1 can be found such that
s1.substring(i, j).equals(s2)
is true.
If s2 is an empty string, then i = 0, j = 0 is one such substring, so contains() returns true.
As it should.
if(String.Contains("")) always should be true, as long as the String is not null.
essentially i want to know if "aString" contains "String".
Yes, "aString" as a string-value does contain the string-value of "String"
My issue is when comparing say "aS" (a substring of "aString") "aS".contains("String") shows true.
Are you sure? This cannot be, therefore I rather suspect bugs in your code.
To spare youself of "empty String symbols" consider this:
try {
File file = new File("symbolTable.txt");
Scanner scanner=new Scanner(file);
while (scanner.hasNextLine()) {
// toLowerCase will do nothing for characters that are not letters
// Don't spend CPU cycles with regex
String symbolLine=scanner.nextLine().toLowerCase();
// Collect the symbol only if non-empty?? This will save you from empty symbols
if(symbolLine.trim().length()>0) {
symbolTable.add(symbolLine); // or .add(symbolLine.trim()) ???
}
}
scanner.close();
} catch (Exception ex) {
ex.printStackTrace();
}
You may have to look at this one a bit mathematically to see why s.contains("") is always true. Suppose you think of this this way:
a.contains(b) is true if there are some values i and j such that a.substring(i,j) is equal to b.
If you think about it a bit, you'll see that this is exactly what contains means when the argument is a nonempty string like "xyz". If there is some substring of x that equals "xyz", then s.contains("xyz") is true. If there is no such substring, then s.contains("xyz") is false.
So it makes sense that the same logic would apply for an empty string, since it applies everywhere else. And it's always true that a.substring(0,0) equals "" (if a is not null). That's why a.contains("") should always be true.
It may not be intuitively obvious from the English meaning of "contains", but when you're dealing with "edge cases" like this, you sometimes have to think in different terms. Often, the Javadoc spells things out so that you can easily figure out what happens in the edge cases, without relying on intuition. Unfortunately, in this case, they didn't.
Related
I have been trying to get my try/catch set up to work but it doesn't seem to run either the try section or the catch section and just returns the default value of the variable.
I had it working before and cant remember what it was that i changed because I haven't touched it for a while
i can include the data file if requested
Any ideas?
package firsttry;
import java.io.File;
import java.io.FileNotFoundException;
import java.util.InputMismatchException;
import java.util.Scanner;
public class csv{
public double speed(int tool , int block){
double blockbreak = 0;
//Define file variable thing
//runs through file
try {
String filename = "data.csv";
File file = new File(filename);
Scanner inputStream = new Scanner(file);
//runs through each line as long as there is something next
while (inputStream.hasNext()){
String data = inputStream.next();//gets a whole line
String[] values = data.split(",");
if (values[1].equals(block)){
blockbreak = Double.parseDouble(values[tool + 2]);
System.out.println(blockbreak);
blockbreak = 4;
}
}
}catch (Exception e) {
System.out.println("ERROR");
blockbreak = 4;
}
return blockbreak;
}
public String name(int block){
String filename = "data.csv";
File file = new File(filename);
//runs through file
try {
Scanner inputStream = new Scanner(file);
//runs through each line as long as there is something next
while (inputStream.hasNext()){
String data = inputStream.next();//gets a whole line
String[] values = data.split(",");
if (values[1].equals(block)){
//int speed = Integer.parseInt(values[tool]);
String blockname = values[0];
return blockname;
}
}
} catch (FileNotFoundException e) {
}
return filename;
}
}
Don't have enough reputation to comment, so writing here.
You should modify your if condition in each function() written above,
if (values[1].equals(block)){
}
It will not give you an output you are expecting.
Comparing string with int is incorrect, for example
System.out.println("1".equals(1)); -> will print false
You are observing that the default value is being returned.
Does this mean that your function returns 0? (As initialized here? double blockbreak = 0;)
If that is the case, you should look into what happens in your loop.
This if statement looks dodgy.
if (values[1].equals(block))
What do you expect to happen?
Also, please post a line that matches the if statement and a line that doesn't, and the expected output from the function.
Possible reasons why you only get the default value:
data.csv is an empty file.
values[1].equals(block) returns false. (Which will always be the case since you're comparing a String to an int.)
catch (FileNotFoundException e) doesn't do anything, so you wouldn't know if the file was not found.
To elaborate on point 2, consider values[1].equals(String.valueOf(block))
Let me suggest some troubleshooting tips.
Write a unit test so you can easily run this repeatedly.
Put a System.out.println into the code in a few places to see which places it hits and when (On small problems this is often easier than debugging if you don't typically debug, I often have it print out a letter at the beginning of any code that comes after a decision point like if, loop and try/catch constructs.)
Print out the value of each line as you read it.
Print the value of blockbreak
I would guess your loop or the if statement aren't executing. Printing some values will tell you this quickly.
Also, if you truly intend Blockbreak to be assigned a value, try NOT assigning a default value of 0 in the beginning. This will stop you from compiling until you have assigned a value in every possible program flow path--a very handy feature (May not help in your case because of the way your while loop is structured, but it's a useful habit not to assign initial values until you need to in Java).
I am using 'java.util.Scanner' to read and scan for keywords and want to print the previous 5 lines and next 5 lines of the encountered keyword, below is my code
ArrayList<String> keywords = new ArrayList<String>();
keywords.add("ERROR");
keywords.add("EXCEPTION");
java.io.File file = new java.io.File(LOG_FILE);
Scanner input = null;
try {
input = new Scanner(file);
} catch (FileNotFoundException e) {
e.printStackTrace();
}
int count = 0;
String previousLine = null;
while(input.hasNext()){
String line = input.nextLine();
for(String keyword : keywords){
if(line.contains(keyword)){
//print prev 5 lines
system.out.println(previousLine); // this will print only last previous line ( i need last 5 previous lines)
???
//print next 5 lines
system.out.println(input.nextLine());
system.out.println(input.nextLine());
system.out.println(input.nextLine());
system.out.println(input.nextLine());
system.out.println(input.nextLine());
}
previousLine = line;
}
any pointers to print previous 5 lines..?
any pointers to print previous 5 lines..?
Save them in an Dequeue<String> such as a LinkedList<String> for its "First In First Out (FIFO)" behavior.
Either that or use 5 variables or an array of 5 Strings, manually move Strings from one slot or variable to another, and then print them.
If you use Dequeue/LinkedList, use the Dequeue's addFirst(...) method to add a new String to the beginning and removeLast() to remove the list's last String (if its size is > 5). Iterate through the LinkedList to get the current Strings it contains.
Other suggestions:
Your Scanner's check scanner.hasNextXXX() method should match the get method, scanner.nextXXX(). So you should check for hasNextLine() if you're going to call nextLine(). Otherwise you risk problems.
Please try to post real code here in your questions, not sort-of, will never compile code. i.e., system.out.println vs System.out.println. I know it's a little thing, but it means a lot when others try to play with your code.
Use ArrayList's contains(...) method to get rid of that for loop.
e.g.,
LinkedList<String> fivePrevLines = new LinkedList<>();
java.io.File file = new java.io.File(LOG_FILE);
Scanner input = null;
try {
input = new Scanner(file);
} catch (FileNotFoundException e) {
e.printStackTrace();
}
while (input.hasNextLine()) {
String line = input.nextLine();
if (keywords.contains(line)) {
System.out.println("keyword found!");
for (String prevLine : fivePrevLines) {
System.out.println(prevLine);
}
} else {
fivePrevLines.addFirst(line);
if (fivePrevLines.size() > 5) {
fivePrevLines.removeLast();
}
}
}
if (input != null) {
input.close();
}
Edit
You state in comment:
ok i ran small test program to see if the contains(...) method works ...<unreadable unformatted code>... and this returned keyword not found...!
It's all how you use it. The contains(...) method works to check if a Collection contains another object. It won't work if you feed it a huge String that may or may not use one of the Strings in the collection, but will work on the individual Strings that comprise the larger String. For example:
ArrayList<String> temp = new ArrayList<String>();
temp.add("error");
temp.add("exception");
String s = "Internal Exception: org.apache.tomcat.dbcp.dbcp.SQLNestedException: Cannot get a connection, pool error Timeout waiting for idle object";
String[] tokens = s.split("[\\s\\.:,]+");
for (String token : tokens) {
if (temp.contains(token.toLowerCase())) {
System.out.println("keyword found: " + token);
} else {
System.out.println("keyword not found: " + token);
}
}
Also, you will want to avoid posting code in comments since they don't retain their formatting and are unreadable and untestable. Instead edit your original question and post a comment to alert us to the edit.
Edit 2
As per dspyz:
For stacks and queues, when there isn't any significant functionality/performance reason to use one over the other, you should default to ArrayDeque rather than LinkedList. It's generally faster, takes up less memory, and requires less garbage collection.
If your file is small (< a million lines) you are way better off just copying the lines into an ArrayList and then getting the next and previous 5 lines using random access into the array.
Sometimes the best solution is just plain brute force.
Your code is going to get tricky if you have two keyword hits inside your +-5 line window. Let's say you have hits two lines apart. Do you dump two 10-line windows? One 12-line window?
Random access will make implementing this stuff way easier.
I'm having trouble printing out the final result without each word being on its own line. The output should be formatted just as the input was. Here is the code I used to read the data and print it:
Scanner sc2 = null;
try {
sc2 = new Scanner(new File(dataFile));
} catch (FileNotFoundException e) {
e.printStackTrace();
}
while (sc2.hasNextLine()) {
Scanner s2 = new Scanner(sc2.nextLine());
boolean b;
while (b = s2.hasNext()) {
String s = s2.next();
System.out.println(pig(s));
}
}
The actual instructions were as follows: "Translate the Declaration of Independence ("declaration.txt") into PigLatin. Try to preserve the paragraphs. There are several ways to do this, but they all use nested loops. You may want to look at nextLine, next, split, or StringTokenizer."
We haven't been taught how to use any of the methods listed there, though.
The println method is short for "print line". It prints the given output to the target output device followed by a newline. Check out the other methods in that class for the solution.
Update
The problem here is that to my knowledge java.util.Scanner throws out the whitespace (delimiter) between words. Check out java.util.StringTokenizer for a similar class that can be configured to return the whitespace characters one at a time.
Im working on the question below and am quite close but in line 19 and 32 I get the following error and cant figure it out.
foreach not applicable to expression type
for (String place: s)
Question:
Tax inspectors have available to them two text files, called unemployed.txt and taxpayers.txt, respectively. Each file contains a collection of names, one name per line. The inspectors regard anyone who occurs in both files as a dodgy character. Write a program which prints the names of the dodgy characters. Make good use of Java’s support for sets.
My code:
class Dodgy {
public static void main(String[] args) {
HashSet<String> hs = new HashSet<String>();
Scanner sc1 = null;
try {sc1 = new Scanner(new File("taxpayers.txt"));}
catch(FileNotFoundException e){};
while (sc1.hasNextLine()) {
String line = sc1.nextLine();
String s = line;
for (String place: s) {
if((hs.contains(place))==true){
System.out.println(place + " is a dodgy character.");
hs.add(place);}
}
}
Scanner sc2 = null;
try {sc2 = new Scanner(new File("unemployed.txt"));}
catch(FileNotFoundException e){};
while (sc2.hasNextLine()) {
String line = sc2.nextLine();
String s = line;
for (String place: s) {
if((hs.contains(place))==true){
System.out.println(place + " is a dodgy character.");
hs.add(place);}
}
}
}
}
You're trying to iterate over "each string within a string" - what does that even mean?
It feels like you only need to iterate over each line in each file... you don't need to iterate within a line.
Secondly - in your first loop, you're only looking at the first file, so how could you possibly detect dodgy characters?
I would consider abstracting the problem to:
Write a method to read a file and populate a hash set.
Call that method twice to create two sets, then find the intersection.
Foreach is applicable for only java.lang.Iterable types. Since String is not, so is the error.
If your intention is to iterate characters in the string, then replace that "s" with "s.toCharArray()" which returns you an array that is java.lang.Iterable.
I am writing a method to search through a dicitionary to find multiple words of the same length that contain the same letter at a set point. I.e. All words of length 5 that have b as their second letter.
I'm writing this method by TDD is eclipse and so far my method is as follows:
private OpenQueue openQueue = new OpenQueue();
private boolean value;
private int lengthOfWord, numberFound;
private File inFile = new File("src/src/WordList"); //This is a text file
public Search(int length) {
this.lengthOfWord = length;
}
public boolean examine2(int crossingPoint, char letter) {
try {
Scanner input = new Scanner(inFile);
while (input.hasNextLine()) { //while there are words left to be read
String word = input.nextLine();
if(word.length() == lengthOfWord) { //if the word is of the right length
while(word.charAt(crossingPoint-1) == letter){
numberFound = numberFound + 1; //number of solutions is increased by one
openQueue.add(word);//word is added to the open queue
value = true; //value is true when at least one solution has been found
}
}
}
} catch (FileNotFoundException e) {
System.out.println("They File was not Found");
e.printStackTrace();
}
System.out.println(numberFound); //returns number of words found
return value; //should return true if there is at least one word
}
For my test I trying to find all five letter words that have a second letter b and there are several words that fit this as I've checked manually. However when I run JUnit it says that it expected true but it was false.
The code runs up to but not past the while(word.charAt(crossingPoint-1) == letter) loop, as previously I added in System.out.println("Here") before this loop to check were the code runs until.
I'm not sure how to fix this in order for the code to run without the test failing. Thanks for your help.
It's hard to look at this code -- arghh! But there appear to be at least one syntax error. I'm not sure whether you just copied it into this question incorrectly, otherwise I don't even see how it can compile. You put parentheses after lengthOfWord which makes it look like a no-argument method or method call, but you appear to want to use it as an integer variable.
Also inFile and numberFound do not appear to be defined. You will have to provide more context.