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how many time the characters of string are to be found in another string

my professor gave me an exercise to find how many time the characters of string called "filter" are to be found in a second string called "query".
before I begin I am java noob and English isnt my native language.
example:
String filter="kjasd";
String query="kjg4t";
Output:2
getting how many times a char has been found in another string isnt my problem but the problem that the professor gave us some rules to stick with:
class filter. The class must be the following public
Provide interfaces:
public Filter (String letters) (→ Constructor of class)
The string representing the filter should be stored in the letters string
public boolean contains (char character)
Returns true if the passed character is contained in the query string, otherwise false
-public String toString ()
Returns an appropriate string representation of the class (just to be clear I have no clue about what does he means with this one!)
To actually determine the occurrences of the filter in the query, another class QueryResolver is to be created.
The class should be able to be used as follows:
QueryResolver resolver = new QueryResolver();
int count = resolver.where(query).matches(filter).count();
the filter and the query are given by the user.
(i couldnt understand this one! )The methods "where" and "matches" configure the "QueryResolver" to include a subsequent call of "count" the calculation based on the previously passed variables
"query" and "filter" performs.
The count method should use the filter's previously-created method.
The modifier static is not allowed to use!
I dunno if he means that we cant use static {} or we cant use public (static) boolean contains (char character){}
we are not allowed to use void
so the problems that encountered me
- I can not pass a char to the method contains as long as it is not static.
error "Non-static variable can not be referenced from a static context"
i did not understand what i should do with the method toStirng!
what I've done so far:
Approach Nr 1:
so I just wrote everything in the main method to check whether the principle of my code works or not and then I wanted to create that whole with constructor and other methods but unfortunately I did not succeed.
Approach Nr 2:
then I tried to write the code in small mthoden as in the exercise but I did not succeed !.
in both aprroaches i violated the exercise rules but i cant seem to be able to do it alone thats why i posted the question here.
FIRST APPROACH:
public class filter{
public filter(String letters) {
//constructor of the class
String filter;
int count;
}
public boolean contains (char character){
/*Subprogram without static!
*the problem that I can't pass any char to this method if it wasn't static
*and I will get the following error"Non-static variable cannot be referenced from a static context"
*I understand why I'm getting the error but I don't know how to get around it X( */
return true ;
}
public String toString (){
/*he told us to include it in the program but honestly, I don't know what shall I write in it -_-
*I make it to null because you have to return something and I don't know what to do yet
*so, for now, I let it null. */
return null;
}
public static void main(String[] args) {
Scanner in =new Scanner (System.in);
System.out.println("please enter the query string! ");
String query= in.next();
System.out.println("please enter the filter stirng!");
String filter= in.next();
System.out.println("the query string is : [" + query+ "]");
System.out.println("the filter string is : [" + filter+ "]");
int count=0;
// I initialized it temporarily because I wanted to print it!
//later I need to use it with the boolean contains as a public method
boolean contains=false;
//to convert each the query and the filter strings to chars
char [] tempArray=query.toCharArray();
char [] tempArray1=filter.toCharArray();
//to iterate for each char in the query string!
for (int i = 0; i < tempArray.length; i++) {
char cc = tempArray[i];
//to iterate for each char in the filter string!
for (int j = 0; j < tempArray1.length; j++) {
// if the value in the filter string matches the value in the temp array then increment the counter by one!
if(tempArray1[j] == cc){
count++;
contains=true;
}
}
}
System.out.println("the characters of the String ["+filter+"] has been found in the forworded string ["+query+"] exactly "+count+" times!" );
System.out.println("the boolean value : "+ contains);
in.close();
}
}
SECOND APPROACH
- But here too I violated the rules of the task quite brutally :(
- First, I used void and did not use the tostring method.
- Second, I did not use a constructor.
- I did not add comments because that's just the same principal as my first attempt.
public class filter2 {
public static void main(String[] args) {
Scanner in = new Scanner (System.in);
System.out.println("enter the filter string:");
String filterStr=in.next();
System.out.println("enter the query string:");
String querystr =in.next();
Filter(filterStr, querystr);
in.close();
}
public static void Filter(String filterstr , String querystr){
char [] tempArray1 = filterstr.toCharArray();
contains(tempArray1, querystr);
}
public static void contains(char[]tempArray1, String querystr){
boolean isThere= false ;
int counter=0;
char [] tempArray = querystr.toCharArray();
for (int i = 0; i < tempArray.length; i++) {
char cc = tempArray[i];
for (int j = 0; j < tempArray1.length; j++) {
if(tempArray1[j] == cc){
counter++;
isThere=true;
}
}
}
System.out.println("the letters of the filter string has been found in the query string exactly "+counter+" times!\nthus the boolean value is "+isThere);
}
/*
* sadly enough i still have no clue what is meant with this one nor whatshall i do
* public String toString (){
* return null;
* }
*
*/
}
Few hints and advice would be very useful to me but please demonstrate your suggestions in code because sometimes it can be difficult for me to understand what you mean by the given advice. ;)
Thank you in advance.
(sorry for the gramatical and the type mistakes; english is not my native language)

As already mentioned, it is important to learn to solve those problems yourself. The homework is not for punishment, but to teach you how to learn new stuff on your own, which is an important trait of a computer scientist.
Nonetheless, because it seems like you really made some effort to solve it yourself already, here is my solution, followed by some explanation.
General concepts
The first thing that I feel like you didn't understand is the concept of classes and objects. A class is like a 'blueprint' of an object, and the object is once you instanciated it.
Compared with something like a car, the class would be the description how to build a car, and the object would be a car.
You describe what a class is with public class Car { ... }, and instanciate an object of it with Car myCar = new Car();.
A class can have methods(=functions) and member variables(=data).
I just repeat those concepts because the code that you wrote looks like you didn't fully understand that concept yet. Please ask some other student who understood it to help you with that.
The Filter class
public class Filter{
String letters;
public Filter(String letters) {
this.letters = letters;
}
public boolean contains (char character){
for(int i = 0; i < letters.length(); i++) {
if(letters.charAt(i) == character)
return true;
}
return false;
}
public String toString (){
return "Filter(" + letters + ")";
}
}
Ok, let's brake that down.
public class Filter{
...
}
I guess you already got that part. This is where you describe your class structure.
String letters;
This is a class member variable. It is unique for every object that you create of that class. Again, for details, ask other students that understood it.
public Filter(String letters) {
this.letters = letters;
}
This is the constructor. When you create your object, this is the function that gets called.
In this case, all it does is to take an argument letters and stores it in the class-variable letters. Because they have the same name, you need to explicitely tell java that the left one is the class variable. You do this by adding this..
public boolean contains (char character){
for(int i = 0; i < letters.length(); i++) {
if(letters.charAt(i) == character)
return true;
}
return false;
}
This takes a character and looks whether it is contained in this.letters or not.
Because there is no name collision here, you can ommit the this..
If I understood right, the missing static here was one of your problems. If you have static, the function is class-bound and not object-bound, meaning you can call it without having an object. Again, it is important that you understand the difference, and if you don't, ask someone. (To be precise, ask the difference between class, object, static and non-static) It would take too long to explain that in detail here.
But in a nutshell, if the function is not static, it needs to be called on an object to work. Look further down in the other class for details how that looks like.
public String toString (){
return "Filter(" + letters + ")";
}
This function is also non-static. It is used whenever the object needs to be converted to a String, like in a System.out.println() call. Again, it is important here that you understand the difference between class and object.
The QueryResolver class
public class QueryResolver {
Filter filter;
String query;
public QueryResolver where(String queryStr) {
this.query = queryStr;
return this;
}
public QueryResolver matches(String filterStr) {
this.filter = new Filter(filterStr);
return this;
}
public int count() {
int result = 0;
for(int i = 0; i < query.length(); i++) {
if(filter.contains(query.charAt(i))){
result++;
}
}
return result;
}
}
Again, let's break that down.
public class QueryResolver {
...
}
Our class body.
Note that we don't have a constructor here. It is advisable to have one, but in this case it would be an empty function with no arguments that does nothing, so we can just leave it and the compiler will auto-generate it.
public QueryResolver where(String queryStr) {
this.query = queryStr;
return this;
}
This is an interesting function. It returns a this pointer. Therefore you can use the result of the function to do another call, allowing you to 'chain' multiple function calls together, like resolver.where(query).matches(filter).count().
To understand how that works requires you to understand both the class-object difference and what exactly the this pointer does.
The short version is that the this pointer is the pointer to the object that our function currently lives in.
public QueryResolver matches(String filterStr) {
this.filter = new Filter(filterStr);
return this;
}
This is almost the same as the where function.
The interesting part is the new Filter(...). This creates the previously discussed Filter-object from the class description and puts it in the QueryResolver object's this.filter variable.
public int count() {
int result = 0;
for(int i = 0; i < query.length(); i++) {
if(filter.contains(query.charAt(i))){
result++;
}
}
return result;
}
Iterates through the object's query variable and checks for every letter if it is contained in filter. It keeps count of how many times this happens and returns the count.
This function requires that filter and query are set. Therefore it is important that before someone calls count(), they previously call where(..) and matches(..).
In our case, all of that happens in one line, resolver.where(query).matches(filter).count().
The main function
I wrote two different main functions. You want to test your code as much as possible during development, therefore the first one I wrote was a fixed one, where you don't have to enter something manually, just click run and it works:
public static void main(String[] args) {
String filter="kjasd";
String query="kjg4t";
QueryResolver resolver = new QueryResolver();
int count = resolver.where(query).matches(filter).count();
System.out.println(count);
}
Once you understand the class-object difference, this should be straight forward.
But to repeat:
QueryResolver resolver = new QueryResolver();
This creates your QueryResolver object and stores it in the variable resolver.
int count = resolver.where(query).matches(filter).count();
Then, this line uses the resolver object to first call where, matches, and finally count. Again, this chaining only works because we return this in the where and matches functions.
Now finally the interactive version that you created:
public static void main(String[] args) {
Scanner in =new Scanner(System.in);
System.out.println("please enter the query string! ");
String query= in.next();
System.out.println("please enter the filter stirng!");
String filter= in.next();
System.out.println("the query string is : [" + query+ "]");
System.out.println("the filter string is : [" + filter+ "]");
QueryResolver resolver = new QueryResolver();
int count = resolver.where(query).matches(filter).count();
System.out.println("the characters of the String ["+filter+"] has been found in the forworded string ["+query+"] exactly "+count+" times!" );
in.close();
}

Set variable to reference another variable, Java

In Android Studio, I have two array lists with a custom object
ArrayList<MenuMaker> consessionlist = new ArrayList<MenuMaker>();
ArrayList<MenuMaker> entrylist = new ArrayList<MenuMaker>();
And have a few voids that depending on which mode we are in, it needs to use one ArrayList or the other:
private void createMenuButtons()
{
int FoodSize = consessionlist.size();
...
I realize I could do an if statement that if mode = 0 use consessionlist, else use entrylist, but is there a way to say
private void setmode(mode)
{
if (mode == 0){
menulist = consessionlist;
}
else
{
menulist = entrylist;
}
}
private void createMenuButtons()
{
int FoodSize = menulist.size();
...
*Pass-by-reference vs pass-by-value seem to kick my butt on the Oracle test.

I thought I would have to use an if statement overtime I need to choose or have to add some weird complexity, but thus far its actually working as I wanted it to.

Am I returning the correct value from my method & am I writing it correctly?

I'll preface my question with the statement that I am very new to Java, so I apologise if my code is totally disgusting to read.
What I'm trying to do: I'm writing a program that takes two integers from the user, a low value and a high value, and sends both integers to two different methods. Method #1 has a simple for loop and should print out all of the numbers between the lowest number and the highest number that are multiples of 3 or 5, and Method #2 does the same except for numbers that are multiples of 3 or 5 it also checks if that number is also a multiple of 6 and, if so, it prints the number and an asterisk next to it.
What I'm having trouble with: I'm pretty stumped on what I need to return from my methods & how to return anything at all. This is the first time I've worked on a method properly (just moved up from "Hello World) and from what I can see I don't really need to return anything at all. All the code that I've put in my methods pretty much complete the program, so I thought maybe returning the integers I sent would be enough, apparently it's not. So, without further ado, here's my code.
The Error:
javac BonusQ.java
.\MethodOne.java:19: error: illegal start of type
return(int lowestRange, int highestRange);
^
.\MethodTwo.java:36: error: illegal start of type
return(int lowestRange, int highestRange);
^
The Main:
import java.util.Scanner;
public class BonusQ
{
public static void main(String [] args)
{
Scanner scan = new Scanner(System.in);
int lowestRange = 0;
int highestRange = 0;
System.out.println("Enter the lowest integer in your range");
lowestRange = scan.nextInt();
System.out.println("Enter the highest integer in your range");
highestRange = scan.nextInt();
MethodOne.NoAsterisk(lowestRange, highestRange);
MethodTwo.Asterisk(lowestRange, highestRange);
}
}
MethodOne:
public class MethodOne
{
public static int NoAsterisk(int lowestRange, int highestRange)
{
for(int i = lowestRange; i <= highestRange; i++)
{
if (i%5 == 0)
{
System.out.println(i);
}
else if (i%3 == 0)
{
System.out.println(i);
}
}
}
return(int lowestRange, int highestRange);
}
MethodTwo:
public class MethodTwo
{
public static int Asterisk(int lowestRange, int highestRange)
{
for(int i = lowestRange; i <= highestRange; i++)
{
if (i%5 == 0)
{
if (i%5 == 0 && i%6 == 0)
{
System.out.println(i + "*");
}
else
{
System.out.println(i);
}
}
else if (i%3 == 0)
{
if (i%3 == 0 && i%6 == 0)
{
System.out.println(i + "*");
}
else
{
System.out.println(i);
}
}
}
}
return(int lowestRange, int highestRange);
}
Sorry if the post is a bit beefy to read, I just find that adding my thoughts on the code might help you explain to me what's going wrong, seeing as you may not know the extent of my incompetence :)
Thanks in advance.

Ok, Classes have members.
Members are either some variables or arrays of variables
and the methods of a class.
So you got
public class MyMethod
{
public static int Asterisk(int loRange, int hiRange)
{
// Do magic let's make a sum for this example
// You enter loRange and hiRange (you defined it above)
return loRange + hiRange // Here the method returns a result
}
}
// So then....
public static void main(String [] args)
{
// WHATEVER IS IN HERE RUNS ALWAYS FIRST.
z = Asterisk(1,2); // 1 and 2 is lo and hi range values ;)
// Z has a value of 3 now because Asterisk(1,2) returns 1 + 2
}
See how this works?
Now this works because you use the static definition (meaning there must not be an instance of MyMethod created first to use the method. It's not wrong, but if you can make a program do things with class instances, you better do it that way.
You make an instance of a class, this is called an object, using a special method. This method has the exact name of the Class and constructs an instance of it.
You should study now about constructors, abstract classes etc etc.
I can't say you do it wrong or right either. It is about what the program is all about and you should study the scope for variables and methods, and the encapsulation concept of Object Oriented Programming.
Using only static methods, goes against encapsulation principle, it is possibly wrong but I can't tell for sure.
I hope this helped you and gave you a good direction to go on with your study.
PS:
To return multiple results, you should return an array of variables, not just a variable.
You can also return nothing and just have it do the job to a needed array. This FORCES you though to make this array public. (Not a good practice)
Finally if multiple value returns are needed to just print them on the console... well, just do it in the method, no need to return anything really.

You don't need to return anything, being that the methods are printing out all the values.
You can change them into void methods, for example:
public static void asterisk(int lowest, int highest) {
//loops and if statements
//no return statement!
}
The code in the methods will run and voila, you are done!
EDIT: That being said, there's a lot more than can be done to make this code more Java-like, but for now this will work.

mmmmm...you can return types, and (int lowestRange, int highestRange) its not a type. Look at the method definition
public static int Asterisk(int lowestRange, int highestRange)
the return type is declared as int, so you should return an int value. You can do something like
return lowestRange;
return 1;
with that in consideration, the error should dissapear. The question is, why do you need to return a value? From what i've read, your methods are supose to print stuff, not to return stuff...

The return statements are out of the method. You have to put them before the close method brackets.
public class MyClass{
public int sum (int a, int b){
return a + b;
} // The return have to be before this brackets
}

Array in Method Header: error ']' expected (Java)

I'm quite new to arrays and methods, and I've been seeing this error recurring through several programs: error '[' expected.
In each occasion, it seems to correct itself as I adjust something else, but in this particular case, I am completely stumped.
By the way, I am using several methods and arrays to create a quiz (before you ask, yes, this is an assignment and I agree, a list is a better way to handle this data - but that is not an option).
It is possible that I am not passing the arrays correctly between methods, as I'm a little muddy on that process. From my understanding, in order to send/receive (i.e. import/export) an array or other variable between methods, I must declare that variable/array in the method header parameters.
import java.util.Scanner;
public class H7pseudo
{
public static void main(String[] args)
{
//call getAnswerkey method
getAnswerkey(answerkey[i]);
//call getAnswers method
getAnswers(answers[i]);
//call passed method? necessary or no?
boolean passed = passed(answerkey[i], answers[i], qMissed[i], points);
//Print results of grading
if (passed)
{
System.out.println("Congratulations! You passed.");
}
else
{
System.out.println("Try again, sucka. You FAILED.");
}
//call totalPoints
totalIncorrect(points);
//call questionsMissed
questionsMissed(qMissed[i]);
}
//get answer key (create answerkey array & export)
public static void getAnswerkey(answerkey[i])
{
//create answerkey array here
char[] answerkey;
//determine number of questions (indices)
answerkey = new char[20];
//input values (correct answers) for each index
//for our purposes today, the answer is always 'c'.
for (int i = 0; i <=20; i++)
{
answerkey[i] = 'c';
}
}
//get student answers (create answers array & export)
public static void getAnswers(answers[i])
{
//initialize scanner for user input
Scanner scan = new Scanner(System.in);
//create answer array here
char[] answers;
//determine number of questions (indices)
answers = new char[20];
//prompt for user input as values of each index
for (int i = 0; i <= 20; i++) {
answers[i] = scan.nextChar();
}
}
//grade student answers (import & compare index values of arrays:answers&answerkey
//create & export qMissed array
public static boolean passed(answerkey[i], answers[i], qMissed[i], points)
{
int points = 0;
//create new array: qMissed
boolean[] qMissed;
//determine number of questions to be graded
qMissed = new boolean[20];
//initialize values for array
for (int i = 0; i <= 20; i++) {
qMissed[i] = false;
}
//cycle through indices of answerkey[i] & answers[i];
for (int i = 0; i =< 20; i++)
{
if (answers[i] == answerkey[i])
{
correct = true;
points = points+1;
qMissed[i] = true;
}
else {
qMissed[i] = false;
}
}
//evaluate whether or not the student passed (15+ correct answers)
if (points >= 15)
{
passed = true;
}
else
{
passed = false;
}
return passed;
}
public static void totalIncorrect(points)
{
int missed = 20 - points;
System.out.println("You missed " + missed + " questions.");
}
public static void questionsMissed(qMissed[i])
{
// for each index of the array qMissed...
for (int i = 0; i < qMissed.length; i++)
{
//...print correct and false answers.
system.out.println(i + ": " + qMissed[i] + "\n");
}
}
}

You can't define array size in the method signature, in Java.

public static void getAnswerkey(answerkey[i])
You can't put anything inside the [] in a method declaration. Also, you have to mention the type:
public static void getAnswerKey(char[] answerkey)
This is not the only reason your code won't work as intended, but I'll leave the rest as part of the exercise.

Look at your method definitions:
public static void questionsMissed(qMissed[i])
This is wrong. You should define the type of the variable and it should not contain [i] like an element of an array. It should be something like this:
public static void questionsMissed(int qMissed)
Or if you want to pass the array, write it like this:
public static void questionsMissed(int[] qMissed)
Apart of this, there are other several errors in your code:
getAnswerkey(answerkey[i]); //answerkey is not defined
getAnswers(answers[i]); //answers is not defined
It would be better if you start reading a Java tutorial first.

I want to vote up Luiggi's answer, but I don't have enough reputation to do that :)
Congrats, cordivia, on getting started with Java!
Here is how an array is declared:
type[] arrayName = new type[numberOfElements]
For example, you did this right in your method definition for getAnswerkey():
char[] answerkey;
answerkey = new char[20];
The part in the method definition inside the parentheses defines the kind of data the method is willing to accept from the outside. So if you don't need to put something into the method to get something out of it, you don't need to put anything in the parentheses. Define the method like this:
getAnswerkey() {
...But that's not the whole story. If you want to get something out of the method, it needs to have a return type as well. A return type is what you're gonna get out of the method when the method's done doing it's magic. For example, if you want to get an int array out of a method you would do something like this:
public static int getTheInteger() {
Since you want an array of chars from the method, you'll want to do something like this:
public static char[] getAnswerkey() {
So that's how you get a method to give you something back. If don't want anything back, you put void:
public static void noMarshmallows() {
Now, when you use the method, you're gonna need to do something with what it gives you, or it did all that work for nothing. So you need to store the return value in a variable when you call the array (calling methods is what you've been doing in main). You know how to store something in a variable. You use the '=' operator:
int myVeryFavoriteNumber;
myVeryFavoriteNumber = 5;
So, you do the same thing when you're getting something out of an array. You assign the return value to a variable. If you want to do this with an array, do this:
int[] myFavs;
myFavs = getMyFavoriteNumbers();
Same with chars:
char[] answerKey;
answerKey = getAnswerKey();
Voila! Your answer key is now right out in the open for the rest of main to see :)
Now, if you want to put something into a method and have it do something with what you put in, you define a parameter. You know how this works. It's just like declaring a variable, and that's exactly what it is. Parameters go in the parentheses and only the method using the parameter sees that variable name (it's local). Something like this:
public static void plusOneToAll (int[] numbers) {
for (int i = 0; i < numbers.length; i++) {
numbers[i] = numbers[i] + 1;
}
}
Notice int[] numbers in the parentheses. The type being passed in is int[] or integer array. numbers is just the parameter name. It functions just like a variable, but it is declared locally (inside the parentheses) and use locally (inside the method). So, if you wanted to compare the answers from two arrays and return the number of matches (like a total score for instance), you would do something like this:
public static int getTotalScore (char[] correctAnswers, char[] userAnswers) {
int totalScore = 0;
for (int i = 0; i < correctAnswers.length; i++) {
if (userAnswers[i] == correctAnswers[i]) {
totalScore = totalScore + 1;
}
}
return totalScore;
}
Notice the return type: int (written before the method name). Inside the array I'm using the variable totalScore to keep track of the number of times the answers match. The method takes two char arrays from the outside and uses them on the inside. Finally, I return an int: totalScore. That kicks the value of totalScore back out to whatever called it (main).
If I might add one last thing: Do yourself a favor and go pick up a copy of Head First Java. It's hard to find a good tutorial online and Java textbooks are just plain boring. The Head First series are kind of like coloring books for adults.
Best of luck!

java : mapping the Values from Enumeration to Object

I have a Enumeration as shown in below program
public class Test {
public static void main(String args[]) {
Vector v = new Vector();
v.add("Three");
v.add("Four");
v.add("One");
v.add("Two");
Enumeration e = v.elements();
load(e) ; // **Passing the Enumeration .**
}
}
There is also a Student Object
public Student
{
String one ;
String two ;
String three ;
String four ;
}
i need to pass this Enumeration to another method as shown below
private Data load(Enumeration rs)
{
Student stud = new Student();
while(rs.hasMoreElements())
{
// Is it possible to set the Values for the Student Object with appropiate values I mean as shown below
stud.one = One Value of Vector here
stud.two = Two Value of Vector here
stud.three = Three Value of Vector here
stud.four = Four Value of Vector here
}
}
Please share your ideas on this .
Thanks

Sure. You could use the elementAt method, documented here, to get the value you wanted. Do you have a specific reason you are using a Vector? Some of the List implementations might be better.

Enumerations don't have the idea of "first value", "second value", etc. They just have the current value. You could work around this in various ways:
The easy way -- convert it to something easier to work with, like to a List.
List<String> inputs = Collections.list(rs);
stud.one = inputs.get(0);
stud.two = inputs.get(1);
// etc.
Keep track of the position yourself.
for(int i = 0; i <= 4 && rs.hasNext(); ++i) {
// Could use a switch statement here
if(i == 0) {
stud.one = rs.nextElement();
} else if(i == 1) {
stud.two = rs.nextElement();
} else {
// etc.
}
}
I really don't recommend either of these things, for the following reasons:
If you want your parameters in a particular order, just pass them in that way. It's much easier and it's also easier to maintain (and for other people to read).
void example(String one, String two, String three, String four) {
Student student = new Student();
student.one = one;
student.two = two;
// etc.
}
You shouldn't use Enumeration at all, since it's been replaced with Iterator and Iterable since Java 1.2. See ArrayList and Collection.