Why does this program need 2 for loops to function? Is there a way to write this without the 2 for loops?
Its purpose is to assign integer values 1-25 to an array with a length of 25. It then prints the array as five separate lines each containing five array elements separated by commas.
Its output is this:
1,2,3,4,5
6,7,8,9,10
11,12,13,14,15
16,17,18,19,20
21,22,23,24,25
public class ArrayNums
{
static int[] arrayList = new int[25];
public static void main(String[] args)
{
for(int i=0; i<25; i++)
arrayList[i] = i + 1;
printArray();
}
public static void printArray()
{
int i;
for(i=1; i<=25; i++){
if (i % 5 != 0)
System.out.print(arrayList[i-1]+",");
else
System.out.println(arrayList[i-1]);
}
}
}
Of course, the main function would go like this :
public static void main(String[] args)
{
for(int i=0; i<25; i++){
arrayList[i] = i + 1;
if ((i+1) % 5 != 0)
System.out.print(arrayList[i]+",");
else
System.out.println(arrayList[i]);
}
}
Though, it's considered better practice to have one function doing only one thing at a time. It makes it much easier to understand, hence your first version I would rather advice to use.
Keep it separate because this enables Separation of Concerns and better usage and maintenance of the program. As #cricket_007 stated, it's better to "have buildArray() as a separate function from printArray()".
In this scenario, the output could be achieved using a single loop and you could print i instead of the arrayList contents, but I doubt you really have a critical need to print 1 to 25 on 5 lines - assume the build and print functions would change in practice. Consider a few scenarios:
Scenario 1
Let's say the program was later required to also output to a CSV file and return a JSON object (not at the same time but by different function calls). If you're building and printing in the same loop, now you need to put the building part into three different functions.
Scenario 2
Let's say you need to change the contents of the array from numbers to letters or inputted data or the ability for the program to do any of those three. Making this change within the loop makes it harder to see potential conflicts or errors.
Scenario 3
Both Scenario 1 and Scenario 2 happen.
I think this will help you.`You could easily add the printarray() method inside the first method.
public static void main(String[] args) {
for(int i=1;i<=25;i++){
arrayList[i-1]=i;
if(i%5==0){
System.out.println(i);
}else{
System.out.print(i+",");
}
}
}
Related
I'm fairly new to coding and am struggling with an assignment for my class. The program takes a user input for the size of an Array and prompts the user to enter each value 1 at a time. The array size starts at 3 and if the array needs to be bigger when the array has filled a new array that's 2x size is created and all info is copied into it. I was able to figure out this part but I just can't see what I'm doing wrong in the downsizing part. After the info is copied I have to remove the trailing zeroes. I think I have the downsize method right but I don't know if I'm calling it right
import java.util.Scanner;
public class Lab6 {
public static void main(String args[]) {
int[] myarray = new int[3];
int count = 0;
int limit, limitcount = 1;
Scanner kbd = new Scanner(System.in);
System.out.print("How many values would you like to enter? ");
limit = kbd.nextInt();
while (limitcount <= limit) {
System.out.println("Enter an integer value ");
int input = kbd.nextInt();
limitcount++;
if (count < myarray.length) {
myarray[count] = input;
}
else {
myarray = upsize(myarray);
myarray[count] = input;
}
count++;
}
myarray = downsize(myarray, count)
printArray(myarray);
System.out.println("The amount of values in the arrays that we care about is: " + count);
}
static int[] upsize(int[] array) {
int[] bigger = new int[array.length * 2];
for (int i =0;i<array.length; i++) {
bigger[i] = array[i];
}
return bigger;
}
static void printArray( int[] array ) {
for ( int number : array ) {
System.out.print( number + " ");
}
System.out.println();
}
static int[] downsize(int[] array,int count) {
int[] smaller = new int[count];
for (int i =0; i<count; i++) {
smaller[i] = array[i];
}
return array;
}
}
Giving you a full response rather than a comment since you're new here and I don't want to discourage you with brevity which could be misunderstood.
Not sure what happened to your code when you pasted it in here, you've provided everything but the format is weird (the 'code' bit is missing out a few lines at the top and bottom). Might be one to double-check before posting. After posting, I see that someone else has already edited your code to fix this one.
You're missing a semi-colon. I'm not a fan of handing out answers, so I'll leave you to find it :) If you're running your code in an IDE, it should already be flagging that one up for you. If you're not, why on earth not??? IntelliJ is free, easy to get going with, and incredibly helpful. There are others out there as well which different folk prefer :) An IDE will help you spot all sorts of useful things quickly.
I have now run your code, and you do have a problem! It's in your final method, downsize(). Look very, very carefully at the return statement ;) Your questions suggests you aren't actually sure whether or not this method is right, which makes me wonder: have you actually run this code with different inputs to see what results you get? Please do that.
Style-wise: blank lines between methods would make the code easier to look at, by providing a visual gap between components. Please be consistent with putting your opening { on the same line as the method signature, and with having spaces between items, e.g. for (int i = 0; i < count; i++) rather than for (int i =0; i<count; i++). The compiler couldn't care less, but it is easier for humans to look at and just makes it look like you did care. Always a good thing!
I think it is awesome that you are separating some of the work into smaller methods. Seriously. For extra brownie points, think about how you could move that while() block into its own method, e.g. private int[] getUserData(int numberOfItems, Scanner scanner). Your code is great without this, but the more you learn to write tiny units, the more favours you will be doing your future self.
Has your class looked at unit testing yet? Trust me, if not, when you get to this you will realise just how important point 5 can be. Unit tests will also help a lot with issues such as the one in point 3 above.
Overall, it looks pretty good to me. Keep going!!!
Simple mistake in your downsize method. If you have an IDE like Eclipse, Intellij, etc. you would have seen it flagged right away.
return array; // should return smaller
I have a few suggestions since you mentioned being new to coding.
The "limitcount" variable can be removed and substituted with "count" at every instance. I'll leave it to you to figure that out.
Try using more descriptive and understandable variable names. Other people will read your code (like now) and appreciate it.
Try to use consistent spacing/indentation throughout your code.
Your upsize method can be simplified using a System.arraycopy() call which generally performs better and avoids the need for writing out a for loop. You can rewrite downsize in a similar manner.
static int[] upsize(int[] array) {
int[] bigger = new int[array.length * 2];
System.arraycopy(array, 0, bigger, 0, array.length);
return bigger;
}
Edit: All good points by sunrise above - especially that you've done well given your experience. You should set up an IDE when you have the time, they're simple to use and invaluable. When you do so you should learn to step through a debugger to explore the state of your program over time. In this case you would have noticed that the myarray variable was never reassigned after the downsize() call, quickly leading you to a solution (if you had missed the warning about an unused "smaller" array).
Say, I'm making a simple badugi card game where the Hand is represented by 10 characters in a string. E.g:
2s3h5dQs - 2 of spades, 3 of hearts, 5 of diamonds, Queen of spades
Now, in this badugi card game I want to create two loops where the first loop checks if all the ranks are different(none of them can be the same) and the other loop checks if all the suits are different. If both of these conditions return as true where they all have different ranks and suits, the hand has drawn a badugi(please excuse my lack of terminology where necessary.)
Now, how can I create an efficient loop for such a situation? I was thinking that I could create several if statements as such:
if (hand.charAt(0) != hand.charAt(2) && hand.charAt(0) != hand.charAt(4) && hand.charAt(0) != hand.charAt(6))
if (hand.charAt(2) != hand.charAt(0) && hand.charAt(2) != hand.charAt(4) && hand.charAt(2) != hand.charAt(6))
... and so forth comparing every single index to one another. But this gets tedious and seems very unprofessional. So my question is, how do I write an efficient loop for this scenario? How can I compare/check if there are no matches at these specific index points to one another?
If I haven't explained properly then please let me know.
Please keep in mind, I am not allowed freedom of how to formulate a hand. It has to be in the format above
You are putting your energy into the wrong place.
You do not need to worry about efficiency at all.
Instead, you should worry about creating a clean design (based on reasonable abstractions) and then write code that is super-easy to read and understand.
And your current approach fails both of those ideas; unfortunately completely.
In other words: you do not represent hands and values as characters within a String.
You create a class that abstracts a Card (with its value and face).
And then a "hand" becomes a List / array of such Card objects. And then you can use concepts such as Comparator to compare card values, or you can make use of equals() ...
And even when you wish to keep your (actually over-complex) naive, simple approach of using chars within a string; then you should at least use some kind of looping so that you don't compare charAt(0) against charAt(2); but maybe charAt(i) against charAt(j).
And following your edit and the excellent comment by jsheeran: even when you are forced to deal with this kind of "string notation"; you could still write reasonable code ... that takes such string as input, but transforms them into something that makes more sense.
For example, the Card class constructor could take two chars for suite/value.
But to get you going with your actual question; you could something like:
public boolean isCardDistinctFromAllOtherCards(int indexToCheck) {
for (int i=0; i<cardString.length-1; i+=2) {
if (i == indexToCheck) {
continue;
}
if (cardString.charAt(indexToCheck) == cardString.charAt(i)) {
return false;
}
}
return true;
}
( the above is just an idea how to write down a method that checks that all chars at 0, 2, 4, ... are not matching some index x).
You should really think about your design, like creating Card class etc., but back to the question now, since it's not gonna solve it.
I suggest adding all 4 values to a Set and then checking if size of the Set is 4. You can even shortcut it and while adding this yourSet.add(element) return false then it means there is already that element in the set and they are not unique. That hardly matters here since you only need to add 4 elements, but it may be useful in the future if you work with more elements.
I would advice creating an array with these chars you are referencing just to clean up the fact you are using indices. i.e create a vals array and a suits array.
This would be my suggestion by using a return or break the loop will stop this means when a match is found it wont have to loop through the rest of the elements .. Hope this helps !
private static int check(char[] vals, char[] suits){
int flag;
for(int i=0; i<=vals.length-2;i++){
for(int k=vals.length-1; k<=0;k++){
if(vals[i]==vals[k]){
flag=-1;
return flag;
}
if(suits[i]==suits[k]){
flag=1;
return flag;
}
}
}
return 0;
}
Why not simply iterate over your string and check for same ranks or suits:
public class NewClass {
public static void main(String[] args) {
System.out.println(checkRanks("2s3h5dQs"));
System.out.println(checkSuits("2s3h5dQs"));
}
public static boolean checkRanks(String hand){
List<Character> list = new ArrayList<>();
for (int i = 0; i< hand.length(); i+=2){
if (!list.contains(hand.charAt(i))){
list.add(hand.charAt(i));
}
else{
return false;
}
}
return true;
}
public static boolean checkSuits(String hand){
List<Character> list = new ArrayList<>();
for (int i = 1; i< hand.length(); i+=2){
if (!list.contains(hand.charAt(i))){
list.add(hand.charAt(i));
}
else{
return false;
}
}
return true;
}
}
Have an assignment I cant figure out. The assignment is:
With a given method:
static void writeTexts(String text, int amount);
Print out the text in the parameter text as many times as given by the variable amount. Every print of text on separate line.
Print an empty line for every third time text is printed.
Write a main method with one or more calls of writeTexts with appropriate test data (don't know what this means) to check that the method works in all cases.
I'm a beginner and find this very difficult, have been reading and watching tutorials, also searched and found a similar question, but can`t seem to grasp this. Any help is appreciated.
The error I get when running my code is:
cannot find symbol.
What I got so far:
public class Task {
static void writeTexts(String text, int amount) {
amount = 0;
text = "hallo";
while (amount< 3) {
System.out.println(text);
amount++;
}
}
public static void main(String[] args) {
writeTexts(text);
}
}
static void writeTexts(String text, int amount) {
for(int i = 0; i < amount; i++){
//Check if the line is the a multiple of 3
//then print an empty line
//I use i + 1 because I start at 0 which is a multiple of 3
//but we are not interested by the that
if( (i + 1) % 3 == 0 ){
System.out.println("");
}
//Print the text
System.out.println(text);
}
Now for calls of writeTexts with appropriate test data that essentially means call the function with so the appropriate parameters e.g: writeText("Halo 3", 3).
I would strongly recommend you to read some more on function to get better grasp of how they work.
You are overwriting amount with 0 and you are overwriting text with "hallo" which is incorrect because you will be printing "hallo" instead of text and you lose track of how many time you need to print.
amount = 0;
text = "hallo";
Your loop will always only iterate 3 times. Instead you should iterate amount times. To do this, you will also need a counter i
int i = 0;
while (i < amount) {
You are not printing an empty line every third time text is printed. You should add this:
i++;
if (amount % 3 == 0) { // If amount is divisible by 3
System.out.println();
}
I want to make a program that each semester, creates a schedule depending of a list of classes I input, so if I add various classes, depending of the time and days that these classes will happen then the program would be able to match what classes can be added without intercepting each other. I want to know if there is an algorithms or way of comparing the class schedule in order to determine what classes can I have from the list of courses.
The only way of doing these that I can imagine is with many if statements or adding an starting course and then having an array that tracks the hours, starting each position at 0 and then each time an hour is occupied I change the array position to 1. Then when adding a course I check what positions are different to 1 and try to add the class.
I want to find a more optimal solution to this problem than the ones I can imagine.
This is a planning problem. Planning problem are very difficult to solve in a efficient way: performance issues arise very quickly in this kind of problem.
If you just want to solve the problem, you should check an existing planning problem solver like OptaPlanner: it's open source, so you can try to understand how it work and there is a blog with interresting thoughts about planning problem.
If you're wanting a method where, given a group of classes with their times and a chosen class, output the available classes, you can use simple iteration to do the job. Suppose you have a 5 hour slot with 4 classes you could represent each class with a single array:
int[][] times = {
{0,1,1,0,0},
{1,1,0,0,0},
{0,1,0,0,0},
{0,0,0,1,1}
};
So if you were to choose the class taking up the last 2hrs then the remaining options would be:
{0,1,1,0,0},
{1,1,0,0,0},
{0,1,0,0,0}
Given this representation you could do something like:
import java.util.*;
public class C {
static int[][] available(int[] c,int[][] times){
ArrayList<Integer> index = new ArrayList<>();
ArrayList<Integer> result = new ArrayList<>();
for(int i=0;i<c.length;i++)
if(c[i]==1) index.add(i);
for(int i = 0; i < times.length; i++){
if(!times[i].equals(c)) {
for (int j = 0; j < times[0].length; j++) {
if(times[i][j]==1){
if(index.contains(j)) break;
}
if(j==times[0].length-1) result.add(i);
}
}
}
int[][] r = new int[result.size()][c.length];
for(int i=0;i<result.size();i++){
r[i] = times[result.get(i)];
}
return r;
}
public static void main(String[] args) {
int[][] times = {
{0,1,1,0,0},
{1,1,0,0,0},
{0,1,0,0,0},
{0,0,0,1,1}
};
int[] c = {0,0,0,1,1};
available(c,times);
System.out.println(Arrays.deepToString(available(c,times)));
}
}
I have a 10x10 multiplication table. I need to code in so that when a user inputs a certain number, 50 for example, the numbers >50 are replaced by a character and the rest remain the same.
I know how to do this using strings but I have no clue how to do this in this situation. Any help will be appreciated.
public class task4{
public static void main(String args[]){
int Multiples = 10;
System.out.format(" Table");
for(int z = 1; z<=Multiples;z++ ) {
System.out.format("%5d",z);
}
System.out.println();
System.out.println("-------------------------------------------------------------------------------------------------------");
for(int i = 1 ;i<=Multiples;i++) {
System.out.format("%5d |",i);
for(int j=1;j<=Multiples;j++) {
System.out.format("%5d",i*j);
}
System.out.println();
}
}
}
That seems to be simple enough problem, basically you have table drawing code, your for loops, so we function that off into a nice little method public void drawTable(){} which we call to draw the table initially, but we also provide an overloaded version which takes a number public void drawTable(int maxDispNum){} and this method is the same except if i*j >maxDispNum we print a character instead. then in main we can simply while(true){ read val; drawTable(val);}
alternativley if you want to maintain a permanent record of what's been removed stored the table in an array, 10*10 in your case and use some marker, -1 works here to indicate removed, and simply check for that in your draw method,