This question already has answers here:
Java: join array of primitives with separator
(9 answers)
What's the simplest way to print a Java array?
(37 answers)
Closed 2 years ago.
I'm creating a class with a char[] array as the only instance variable. I have to use a constructor and accesor methods and such but the difficult part is creating an efficient toString() method.
Right now, I've initialized the array as:
private char[] tune = new char[5];
My toString() method looks like this:
public String toString() {
return notes[0] + " " + notes[1] + " " + notes[2] + " " + notes[3] + " " + notes[4];
}
My question is: Is there a more efficient method of printing this. I thought of using a for loop, as shown below:
for(int i = 0; i <= tune.length; i++) {
return tune[i] + " ";
}
but I assume that would return tune[0] and just stop.
If you want to override the toString() method, use a StringBuilder which is initialized outside the loop.
public String toString() {
StringBuilder sb = new StringBuilder();
for (char ch : array) { // you used both notes and tune arrays in your examples,
// so I'm just going to use "array" as the variable name as an example
sb.append(ch);
sb.append(" ");
}
return sb.toString();
}
Note that this will cause an extra space at the end, if this is not wanted, use this instead:
public String toString() {
StringBuilder sb = new StringBuilder();
for (int i = 0; i < array.length - 1; i++) { // adds a space after every element
// except for the last one, hence "i < array.length - 1"
sb.append(array[i] + " ");
}
sb.append(array[array.length - 1]); // adds only the last element and no space
// after
return sb.toString();
}
Hope this is easy to understand!
NOTE - Java can already convert the char[] to string, but I'm assuming you want to change the way it does that.
Arrays already have built in methods to print out the entire Array. (Not the case for ArrayLists).
If you look in the documentation for Arrays, you can see that there is a function called Arrays.toString()
Here is an example of how you can use it.
String[] array = new String[] {"a","b","c"};
// Print out the Array
System.out.println(Arrays.toString(array));
// Output
[a,b,c]
If you would like to print out an array from index a to index b, then using a for... loop would be better.
Related
This question already has answers here:
Reverse a string in Java
(36 answers)
Closed 5 years ago.
I can't get my function to return the reversed string. I keep getting the original string, plus the reversed sting attached together.
P.S this is obviously a question from someone new. Cut me some slack and save me from the horribly demoralizing down vote.
int i;
reverse = reverse.replaceAll("[^a-zA-Z]+", "").toLowerCase();
for (i = reverse.length() - 1; i >= 0; i--) {
reverse = reverse + reverse.charAt(i);
}
return reverse;
}
You need another String (or some other method / memory) to build your return value (consider "a", starting from the end of the String add "a" - thus you get "aa"). Instead, I would use a StringBuilder - and the entire method might be written like
return new StringBuilder(reverse.replaceAll("[^a-zA-Z]+", "")
.toLowerCase()).reverse().toString();
Change the snippet to,
String reverse_string="";
for (i = reverse.length() - 1; i >= 0; i--) {
reverse_string += reverse.charAt(i);
}
return reverse_string;
You will need a separate String variable to contsruct the newly reversed string.
Why not just let the existing Java api do this for you?
String someString = "somestring123";
System.out.println(new StringBuilder(someString).reverse().toString());
output:
StringBuilder
OK so I'm trying to design a simple program that checks to see if a substring of length 4 characters is within all initial strings. Here is my code as follows:
public class StringSearch{
private String[] s1Array = {"A","C","T","G","A","C","G","C","A","G"};
private String[] s2Array = {"T","C","A","C","A","A","C","G","G","G"};
private String[] s3Array = {"G","A","G","T","C","C","A","G","T","T"};
//{for (int i = 0; i < s1Array.length; i++){
// System.out.print(s1Array[i]);
//}}//check if Array loaded correctly
/**
* This is the search method.
*
* #param length length of sub string to search
* #param count counter for search engine
* #param i for-loop counter
* #return subStr returns strings of length = 4 that are found in all 3 input strings with at most
* one mismatched position.
*/
public String Search()
{
int length = 4;
int count = 0;
int i = 0;
ArrayList<StringSearch> subStr = new ArrayList<StringSearch>();
//String[] subStr = new String[4];
do
{
for (i = count; i < length; i++){
subStr.add(s1Array[i]); // cant find .add method???
count = count + 1;
}
if (s2Array.contains(subStr) && s3Array.contains(subStr)){ //can't find .contains method???
System.out.println(subStr + "is in all 3 lists.");
}
if (count = s1Array.length){
System.out.println("Task complete.");
}
else{
count = count - length;
count = count + 1;
}
}while (count <= s1Array.length);
}
}
For some reason, Java cannot seem to find the .add or .contains methods and I have no idea why. So my approach was to turn the initial Strings each into an array (since the assignment specified each string would be exactly N elements long, in this case N = 10) where 1 letter would be 1 element. The next thing I did was set up a for loop that would scan s1Array and add the first 4 elements to an ArrayList subStr which is used to search s2Array and s3Array. Here is where .add isn't a valid method, for whatever reason. Commenting that out and compiling again, I also ran into an issue with the .contains method not being a valid method. Why won't this work? What am I missing? Logically, it seems to make sense but I guess maybe I'm missing something in the syntax? Help would be appreciated, as I'm a Java novice.
There are lots of errors and misunderstandings here.
Let's start with #1
private String[] s1Array = {"A","C","T","G","A","C","G","C","A","G"};
Making an array of strings is just silly, you should either use a single string or an array of characters.
private String s1 = "ACTGACGCAG";
Or
private char[] s1Array = {'A','C','T','G','A','C','G','C','A','G'};
Now #2
ArrayList<StringSearch> subStr = new ArrayList<StringSearch>();
This means you are trying to make an ArrayList that contains objects of type StringSearch. StringSearch is a class that contains your three arrays and your Search function so I don't think this is what you want.
If you wanted to make a list of 3 strings you might do something like this:
ArrayList<String> stringList = new ArrayList<String>();
stringList.add(s1);
stringList.add(s2);
stringList.add(s3);
Now say you defined s1, s2 and s3 as strings you can do something like this.
for(int i = 0; i <= s1.length() - 4; i++)
{
String subStr = s1.substring(i, i + 4);
if(s2.contains(subStr) && s3.contains(subStr))
{
System.out.println(subStr + " is in all 3 lists.");
}
}
System.out.println("Task Complete.");
The above code should achieve what it looks like you are trying to do. However, it should be noted that this isn't the most efficient way, just a way, of doing it. You should start with some more basic concepts judging by the code you have so far.
After declaring subStr as ArrayList you can call add or contains only with StringSearch objects as parameters.
Instead of:
ArrayList<StringSearch> subStr = new ArrayList<StringSearch>();
Replace it with:
String subStr = "";
And within the for loop to get the first 4 letters in s1 to be in its own string (subStr) add the line:
subStr += s1Array[i];
Also, s1Array is a String array, and not a String. The .contains method is a method that belongs to String variables, so for eg. the way you have it implemented, you can say s1Array[i].contains. But you cannot say s1Array.contains. If you change your String arrays to Strings and edit your code to suit, everything should work the way you expect it to work.
First of all you need to educate yourself on the concept of Java generics.
The most basic thing about generics is that once you declare a collection, here it is the arraylist, as you can only add objects of StringSearch.
Second of all, logically what you can do is to implement an algorithm called
Longest Common Subsequence. Check in pairs whether the longest subsequeces are 4 or not on the arrays.
I created a method to output a String. Using the split method and a for loop, I added each word in my sentence into a String array, replacxing the last two letters of each word with "ed". Now, my return statement should return each of the words. When I used System.out.print, it worked. When I use a return and call it in my main method, I get this output: "[Ljava.lang.String;#1b6235b"
The error seems so simple but I just don't know where I'm going worng. Any help would be appreciated.
Here is my method:
public String[] processInfo() {
String sentence = this.phrase;
String[] words = sentence.split(" ");
if (!this.phrase.equalsIgnoreCase("Fred")) {
for (int i = 0; i < words.length; i++) {
words[i] = words[i].substring(0, words[i].length() - 2).concat(
"ed ");
// System.out.print(words[i]);
}
}
return words;
}
You are printing arrays but arrays don't have a proper implementation of toString() method by default.
What you see is
"[Ljava.lang.String;#1b6235b"
This is [Ljava.lang.String; is the name for String[].class, the java.lang.Class representing the class of array of String followed by its hashCode.
In order to print the array you should use Arrays.toString(..)
System.out.println(Arrays.toString(myArray));
A good idea however, it returns my Strings in an Array format. My aim
is to return them back into sentence format. So for example, if my
input is, "Hey my name is Fred", it would output as, "Hed ed naed ed
Fred". Sorry, I forgot to add that it also seperates it with commas
when using Arrays.toString
Then you should modify your processInfo() returning a String or creating a new method that convert your String[] to a String.
Example :
//you use like this
String [] processInfoArray = processInfo();
System.out.println(myToString(processInfoArray));
// and in another part you code something like this
public static String myToString(String[] array){
if(array == null || array.length == 0)
return "";
StringBuilder sb = new StringBuilder();
for(int i=0;i<array.length-1;i++){
sb.append(array[i]).append(" ");
}
return sb.append(array[array.length -1]).toString();
}
As much as I can get from your question and comment is that your aim is to return them back into sentence format. So for example, if your input is, "Hey my name is Fred", it would output as, "Hed ed naed ed Fred".
In that case you should return a String, and not an array. I have modified your method a bit to do so. Let me know if you wanted something else.
public String processInfo() {
String sentence = this.phrase;
String[] words = sentence.split(" ");
if (!this.phrase.equalsIgnoreCase("Fred")) {
sentence = "";
for (int i = 0; i < words.length; i++) {
words[i] = words[i].substring(0, words[i].length() - 2).concat(
"ed ");
sentence += " " + words[i];
// System.out.print(words[i]);
}
}
return sentence.trim();
}
Your commented out call to System.out.print is printing each element of the array from inside the loop. Your method is returning a String[]. When you try to print an array, you will get the java representation of the array as you are seeing. You either need to change your method to build and return a string with all the array entries concatenated together, or your calling code needs to loop through the returned array and print each entry.
I am creating a program that lets you store 10 items in an array. What I haven't been able to get the program to do is give an error if one of the entered items already exists in the array.
So, for example, if the array looks like [banana, potato, 3, 4, yes, ...] and I enter banana again, it should say "Item has already been stored" and ask me to re-enter the value. The code I currently have is:
public static void main(String[] args) {
Scanner keyboard = new Scanner(System.in);
int stringNumber = 0;
String[] stringArray = new String[10];
for (int i = 0; i <= stringArray.length; i++) {
out.println("\nEnter a string");
String input = keyboard.next();
stringArray[stringNumber] = input;
out.println("\"" + stringArray[stringNumber] + "\"" + " has been stored.");
PrintArray(stringArray);
stringNumber++;
You can use nested loops to go through the array to see if the new input exists. It would be better to do this in a function. Also when doing this you need to make sure that you are not at the first element or you will get a null pointer exception.
for (int i = 0; i <= stringArray.length; i++) {
boolean isInArray = false;
System.out.println("\nEnter a string");
String input = keyboard.next();
if (i > 0) {
for (int j = 0; j < stringArray.length; j++) {
if (stringArray[j].equalsIgnoreCase(input)) {
isInArray = true;
break;
}
}
}
if (!isInArray) {
stringArray[stringNumber] = input;
} else {
System.out.println("\"" + stringArray[stringNumber-1] + "\""
+ " has been stored.");
}
PrintArray(stringArray);
stringNumber++;
}
It's always better to use a HashSet when you don't want to store duplicates. Then use HashSet#contains() method to check if element is already there. If ordering is important, then use LinkedHashSet.
If you really want to use an array, you can write a utility method contains() for an array. Pass the array, and the value to search for.
public static boolean contains(String[] array, String value) {
// Iterate over the array using for loop
// For each string, check if it equals to value.
// Return true, if it is equal, else continue iteration
// After the iteration ends, directly return false.
}
For iterating over the array, check enhanced for statement.
For comparing String, use String#equals(Object) method.
When you got the String input, you can create a method that will :
Go through the entire array and check if the string is in it (you can use equals() to check content of Strings)
Returns a boolean value wheter the string is in the array or not
Then just add a while structure to re-ask for an input
Basically it can look like this :
String input = "";
do {
input = keyboard.next();
}while(!checkString(input))
The checkString method will just go through all the array(using a for loop as you did to add elements) and returns the appropriate boolean value.
Without introducing some order in your array and without using an addition structure for instance HashSet, you will have to look through the whole array and compare the new item to each of the items already present in the array.
For me the best solution is to have a helper HashSet to check the item for presence.
Also have a look at this question.
To avoid you should use an Set instead of an array and loop until size = 10.
If you need to keep an array, you can use the .contains() method to check if the item is already present in the array.
while (no input or duplicated){
ask for a new string
if (not duplicated) {
store the string in the array
break;
}
}
You should check the input value in array before inserting into it. You can write a method like exists which accepts String[] & String as input parameter, and find the string into the String array, if it finds the result then return true else false.
public boolean exists(String[] strs, String search){
for(String str : strs){
if(str.equals(search))
return true;
}
return false;
}
performance would be O(n) as it searchs linearly.
I'm trying to display the contents of an ordered array in something like a JTextField.
for (int i=0; i<array.length; i++) {
this.textField.setText(array[i]);
}
This won't work for two reasons. The first minor reason: if the array length is 4 then jtextfield is getting it's value reset 4 times rather than appending each element onto the last.
Second reason: The JTextField only takes strings. I can't find anything I can use in Swing that will let me display integers to the user. Any help?
Quick & Dirty Answer
for (int i=0; i<array.length; i++) {
this.myJTextField.setText(this.myJTextField.getText() + ", " + array[i]);
}
Correct Way
First, calling a member variable JTextField probably isn't wise. Since the class is already called like that, it will confuse readers. Naming conventions in Java state member variables are like myTextField for example. (note: original question changed).
User defined format
Note you can convert any number to a string by simply doing "" + number too. If you have many strings, consider using a string builder, as that's faster and won't update the GUI element multiple times: (also fixes the initial ", " before the first item, which happens above)
StringBuilder builder = new StringBuilder();
for (int i=0; i<array.length; i++) {
builder.append(array[i]));
if(i + 1 != array.length)
builder.append(", ");
}
this.myJTextField.setText(builder.toString());
Canonical array representation
Alternatively, you can use this:
this.myJTextField.setText(Arrays.toString(array));
It will look like [1, 4, 5, 6].
You can concatenate all those integers into a string the then present that value in the textfield.
StringBuilder sb = new StringBuilder();
for( int i : array ) { // <-- alternative way to iterate the array
sb.append( i );
sb.append( ", " );
}
sb.delete(sb.length()-2, sb.length()-1); // trim the extra ","
textField.setText( sb.toString() );
You can use a JTextArea instead of the textfield too.