due to a complex issue which I do not want to enter here, I am not able to count a number of created objects(let's say apples) in a complex Java class, using a simple counter as soon as an apple is created. Therefore I was thinking of an alternativ but do not know how to realize it; if it is at all an option:
A for-loop connected to System.out.println("Apples:" + apples) gives me as many outputs as there are apples. - Which is fine. Now I have to store the number of outputs in a variable - how would you do this - is it possible at all, as the output is displayed in the console?
Thanks in advance!
you can wrap System.out.println() with your own println method that in addition to printing will count, and use that one instead of println in your loop:
private static int counter = 0;
public static void myPrintln(String str) {
counter++;
System.out.println(str);
}
Related
I wrote some code:
public class digitShow {
public static void main(String[] args) {
System.out.println(digitShow(98198187));
}
public static int digitShow(int num) {
if (num != 0) {
System.out.print(num % 10);
return digitShow(num / 10);
} else
return num;
}
}
The code works perfectly fine, but I am trying to make it so instead of printing the numbers in reverse order one by one, the output rather would display each digit one by one in the order that they are entered in the parameter.
So in this case:
1
2
3
4
I've been trying to un-reverse it, but I've had no luck.
Ok, some people on comments are suggesting using arrays or similar. This is correct, however this seems like a question made by someone who is learning recursion (and, as a teacher, I can smell a homework question here).
I will not post the answer because I'd be doing your homework for you and we need good programmers in this world. If I (or anyone else) do your homework you'll never understand the basic concepts of programming, and never becoming a good programmer.
Now, building on top of smac89's comment:
Your code to reverse has an issue: it prints 0 after it reverses the digits. Why? because you are returning an integer and then printing it in your main function but you are not really using the return value anywhere else.
Try calling your method without the System.out.println in main and see what happens.
So, basically, evaluate if you really need to return an integer and, if you don't, you can now evaluate how you are calling the recursion (again, read smac89's comment).
I wish you the best in your studies!
You need to reduce the number by successive divisions first. Then process the values as they are unwound from the stack. This will print the most significant to least significant digit. Then return the starting number.
public static int digitShow(int num) {
if (num > 10) {
digitShow(num/10);
}
System.out.println(num%10);
return num; // returns the starting number.
}
prints
9
8
1
9
8
1
8
7
98198187
This question already has answers here:
How do I create a file and write to it?
(35 answers)
Closed 5 years ago.
I've made a program for determining the time of a murder. The code I have right now prints exactly what it should to the terminal. I want it printed to a file. However, I'm not supposed to use System.setOut() for this assignment. I'm supposed to print to a file instead of to the terminal.
I know how to write a simple String into a file, the problem here is I already have methods for printing my results to the terminal, and I'm not sure how I "convert" those methods into printing into a file instead.
This is my two printing methods and main method:
Printing 2d array method:
public static void printArray2d(String[][] array2d){
for(int i = 0; i < array2d.length; i++){
for(int j = 0; j < array2d[i].length; j++){
System.out.print(array2d[i][j]);
}
System.out.print("\n");
}
}
Printing full report method:
public static void printReport(String[][] array2d, double arrayMin, double arrayMax){
System.out.println("Time since death probability distribution");
double hours = (arrayMax-arrayMin)/(array2d.length-1);
System.out.printf("Each line corresponds to approximately %.2f hours\n", hours);
System.out.printf("%.2f hours\n", arrayMin);
printArray2d(array2d);
System.out.printf("%.2f hours\n", arrayMax);
}
Main method:
public static void main(String args[]) {
double[] array = cooldownSamples(27, 1000);
double[] counts = countsFromArray(array, 20);
String[][] array2d = array2dFromCounts(counts);
printReport(array2d, minFromArray(array), maxFromArray(array));
}
I can post the entire code if needed.
I am aware that there are similar questions asked earlier, but none of them gave me the help I needed. I also do not have enough reputation to ask follow-up questions to any of the answers given on those threads, so I was forced to ask a new question.
Thanks in advance for any help given!
Additional information:
Even though I said I'm not supposed to use System.setOut(), I have tried using the method and answers given in this thread, without any luck. If the best and most efficient way of doing this is via System.setOut(), I do appreciate answers that make me understand how I can implement this and make it work in my code, even though I'm looking for an alternative method.
It is really simple: right now, you are using a (static) object System.out to do all printing. This object has methods to print, println, and so on.
Instead of using System.out, you create an instance of say PrintWriter and call method on that object, like
PrintWriter writer = new PrintWriter("whatever.txt");
writer.println("whatever");
writer.close();
That is all there is to this. Or even simpler, you could instantiate a PrintStream object. You could then do things such as:
PrintStream out = System.out // or new PrintStream("filename");
doStuff(out);
... with:
public void doStuff(PrintStream out) {
out.println...
And now you have one central place where you decided if you want to print to System.out - or somewhere else!
The following requisites are those for the program I'm currently having an issue with:
The program must be able to open any text file specified by the user, and analyze the frequency of verbal ticks in the text. Since there are many different kinds of verbal ticks (such as "like", "uh", "um", "you know", etc) the program must ask the user what ticks to look for. A user can enter multiple ticks, separated by commas.
The program should output:
the total number of tics found in the text
the density of tics (proportion of all words in the text that are tics)
the frequency of each of the verbal tics
the percentage that each tic represents out of all the total number of tics
Here is my program:
public class TextfileHW2 {
// initiate(
public static int[] initiate(int[] values){
for (int z=0; z<keys.length; z++){
values[z] = 0;
}
return values;
processing(values);
}
// processing(values)
public static int[] processing(int[] valuez){
while (input.hasNext()){
String next = input.next();
totalwords++;
for (int x = 0; x<keys.length; x++){
if (next.toLowerCase().equals(keys[x])){
valuez[x]+=1;
}
}
return valuez;
output();
}
for (Integer u : valuez){
totalticks += u;
}
}
public static void output(){
System.out.println("Total number of tics :"+totalticks);
System.out.printf("Density of tics (in percent): %.2f \n", ((totalticks/totalwords)*100));
System.out.println(".........Tick Breakdown.......");
for (int z = 0; z<keys.length; z++){
System.out.println(keys[z] + " / "+ values[z]+" occurences /" + (values[z]*100/totalticks) + "% of all tics");
}
sc.close();
input.close();
}
public static void main(String[] args) throws FileNotFoundException {
static double totalwords = 0; // double so density (totalwords/totalticks) returned can be double
static int totalticks = 0;
System.out.println("What file would you like to open?");
static Scanner sc = new Scanner(System.in);
static String files = sc.nextLine();
static Scanner input = new Scanner(new File(files));
System.out.println("What words would you like to search for? (please separate with a comma)");
static String ticks = sc.nextLine(), tics = ticks.toLowerCase();
static String[] keys = tics.split(",");
static int[] values = new int[keys.length];
initiate(values);
}
My program should be logically right as I wrote it and successfully ran it for a while last week, but the difference with this one (which doesn't work) is that I must use separate methods for each component of the analysis, which shouldn't be too difficult a task considering the program was working before So I naturally tried to split up my program such that I can call my first method (which I called initiate) then my 2nd and 3rd methods called processing and output.
First of all, what does static really mean? I remember my teacher saying that it represents a global variable which I can use anywhere in the program. As you can see I changed every variable to static to perhaps make my task easier.
Also, do I strictly need to use public static + type returned if I'm going to change something?
Let's say I want to change the values of an array (like I do in my program and use public static void) do I need to return something to actually change the values of the array or is it ok to use public static void?
If anyone also has any general pointers for what concerns my methods I would really appreciate it.
Your problem is in your initiate method:
return values;
processing(values);
Once you call return, your method stops. If you are using Eclipse (which I highly recommend), you should have gotten an error saying "Unreachable code," because there is simply no way for the program to execute your processing method.
I also saw this flaw in your output method.
First of all, what does static really mean? I remember my teacher
saying that it represents a global variable which I can use anywhere
in the program. As you can see I changed every variable to static to
perhaps make my task easier.
It depends on the context. There is a good overall description here. The meaning is different when applied to methods, fields, and classes. To say it makes variables "global" is a bit simplified.
Also, do I strictly need to use public static + type returned if I'm going to change something?
I'm a little confused about what you mean. A method declared as public static *return_type* has three separate, independent qualities:
public: It is accessible by any other class.
static: It does not require an instance of the class to function (see above link).
*return_type*: This is, of course, the return type.
These properties aren't really related to "changing something". Unless I misunderstood your question, the answer is: No, the method specifiers and return type have no impact on its ability to change something with the exception that static methods cannot modify non-static fields or call non-static methods of this (there is no this in static methods).
Let's say I want to change the values of an array (like I do in my program and use public static void) do I need to return something to actually change the values of the array or is it ok to use public static void?
What you do in the function is entirely independent of the access specifier and static-ness of it (with the above-mentioned exception that this does not exist in static methods). If your function has any side-effects like changing the values in an array (or any values for that matter), then it does it regardless of public, or static, or its return type.
Check out the More on Classes section of the official language tutorial. It is concise and well-written and should help complete your understanding of the general concepts you're asking about. Check out some of the other tutorials there as well if you'd like.
Ok so i am just learning recursion and i am confused on one point.
This is the code
public class RecursiveDemo {
public static void showRecursion (int num) {
System.out.println("Entering method. num = " + num);
if (num > 1) {
showRecursion(num - 1);
}
System.out.println("Leaving method. num = " + num);
}
public static void main(String[] args){
showRecursion(2);
}
}
The output i am getting is :
Entering method. num = 2
Entering method. num = 1
Leaving method. num = 1
Leaving method. num = 2
My question is why am i getting the output "Leaving method. num = 2". Shouldn't it stop at "Leaving method. num = 1" since num has already reached 1?
Once the original invocation of this method leaves the if statement, it passes to System.out.println("Leaving method. num = " + num);. Since you invoked the message originally with value 2, 2 is the value of num for this part of the code.
Your code runs like this (pseudocode):
Start First Call
if statement
Start Second call
Skips if statement
Print from Second Call
End of Second Call
End of if Statement
Print From First Call
End of First Call
It looks like you have a fundamental misunderstanding of recursion.
When you call your method with (num-1) as arguments, the parent call (the first call, in this case), retains the value num as its argument, which is 2, in this case.
So let's comment out the line below
//showRecursion(num - 1);
What would you get? It must be
Entering method. num = 2
Leaving method. num = 2
And if you uncomment the line above. You should get the one you had.
No.
main will call showRecursion(2), which in turn will call showRecursion(1) (so you get two "Entering" messages). At which point, the condition will fail, so no more recursion occurs. So now the program simply begins returning from each function call in turn, printing both of the "Leaving" messages.
It's because the initial call to showRecursion(2) hasn't finished yet.
Consider the following:
public static void showFirstRecursion (int num) {
System.out.println("Entering method. num = " + num);
if (num > 1) {
showSecondRecursion(num - 1);
}
System.out.println("Leaving method. num = " + num);
}
public static void showSecondRecursion (int num) {
System.out.println("Entering method. num = " + num);
if (num > 1) {
showThirdRecursion(num - 1);
}
System.out.println("Leaving method. num = " + num);
}
// I won't bother showing an implementation for showThirdRecursion, because it won't be called.
public static void main(String[] args){
showFirstRecursion(2);
}
No problem here, right? You'd expect to see the first method entered, second entered, (third not entered because num == 0), second left, first left.
There is really nothing special about recursion. It's just making a function call that happens to be calling the function that the call is a part of. A recursive call behaves, conceptually, in all respects like any other function call. The trick is the design of a recursive algorithm, i.e., coming up with a reason why you'd want to call the same function you're already in.
The other answers already cover the specific question, but here is some information on using a debugger. This tutorial is for Eclipse, but pretty much tells you what you need to know for any visual debugger.
The basics are pretty straightforward, and it would be well worth your time to at least learn how to step through the code. A debugger is an invaluable tool for quickly verifying the logic of your program, and is far easier than scattering print statements everywhere.
Try "showRecursion(5);".
[Answer: This is recursion. There's more than one copy of the variable "num" in memory. "num" is a parameter; it's not a field, and it's not static.]
So what I understood was
with every method call, Stack is getting populated ie. 2,1
but when i>1 doesn't matches it returns/breaks the call and control is given to the system.out.println line, that prints the value starting from the top of stack ie 1,2
public boolean catDog(String str)
{
int count = 0;
for (int i = 0; i < str.length(); i++)
{
String sub = str.substring(i, i+1);
if (sub.equals("cat") && sub.equals("dog"))
count++;
}
return count == 0;
}
There's my code for catDog, have been working on it for a while and just cannot find out what's wrong. Help would be much appreciated!*/
EDIT- I want to Return true if the string "cat" and "dog" appear the same number of times in the given string.
One problem is that this will never be true:
if (sub.equals("cat") && sub.equals("dog"))
&& means and. || means or.
However, another problem is that your code looks like your are flailing around randomly trying to get it to work. Everyone does this to some extent in their first programming class, but it's a bad habit. Try to come up with a clear mental picture of how to solve the problem before you write any code, then write the code, then verify that the code actually does what you think it should do and that your initial solution was correct.
EDIT: What I said goes double now that you've clarified what your function is supposed to do. Your approach to solving the problem is not correct, so you need to rethink how to solve the problem, not futz with the implementation.
Here's a critique since I don't believe in giving code for homework. But you have at least tried which is better than most of the clowns posting homework here.
you need two variables, one for storing cat occurrences, one for dog, or a way of telling the difference.
your substring isn't getting enough characters.
a string can never be both cat and dog, you need to check them independently and update the right count.
your return statement should return true if catcount is equal to dogcount, although your version would work if you stored the differences between cats and dogs.
Other than those, I'd be using string searches rather than checking every position but that may be your next assignment. The method you've chosen is perfectly adequate for CS101-type homework.
It should be reasonably easy to get yours working if you address the points I gave above. One thing you may want to try is inserting debugging statements at important places in your code such as:
System.out.println(
"i = " + Integer.toString (i) +
", sub = ["+sub+"]" +
", count = " + Integer.toString(count));
immediately before the closing brace of the for loop. This is invaluable in figuring out what your code is doing wrong.
Here's my ROT13 version if you run into too much trouble and want something to compare it to, but please don't use it without getting yours working first. That doesn't help you in the long run. And, it's almost certain that your educators are tracking StackOverflow to detect plagiarism anyway, so it wouldn't even help you in the short term.
Not that I really care, the more dumb coders in the employment pool, the better it is for me :-)
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vag qvssrerapr = 0;
sbe (vag v = 0; v < fge.yratgu() - 2; v++) {
Fgevat fho = fge.fhofgevat(v, v+3);
vs (fho.rdhnyf("png")) {
qvssrerapr++;
} ryfr {
vs (fho.rdhnyf("qbt")) {
qvssrerapr--;
}
}
}
erghea qvssrerapr == 0;
}
Another thing to note here is that substring in Java's built-in String class is exclusive on the upper bound.
That is, for String str = "abcdefg", str.substring( 0, 2 ) retrieves "ab" rather than "abc." To match 3 characters, you need to get the substring from i to i+3.
My code for do this:
public boolean catDog(String str) {
if ((new StringTokenizer(str, "cat")).countTokens() ==
(new StringTokenizer(str, "dog")).countTokens()) {
return true;
}
return false;
}
Hope this will help you
EDIT: Sorry this code will not work since you can have 2 tokens side by side in your string. Best if you use countMatches from StringUtils Apache commons library.
String sub = str.substring(i, i+1);
The above line is only getting a 2-character substring so instead of getting "cat" you'll get "ca" and it will never match. Fix this by changing 'i+1' to 'i+2'.
Edit: Now that you've clarified your question in the comments: You should have two counter variables, one to count the 'dog's and one to count the 'cat's. Then at the end return true if count_cats == count_dogs.