如何解决此运行时错误？

Question

I am trying to make a java program which will find and remove repetative characters in string. Like if user types "baloon", the output should be "balon". I used String variable for input and copied its content to Char array so that I can analyze each character. I get ArrayIndexOutOfBoundsException. Here is my code

class doubleKiller{

private String inputStr = " ";
private char[] catchStr = new char[inputStr.length()];
private String modifiedStr;

//Accessor method
public void getString(String inputStr)
{
    this.inputStr = inputStr;
}

public String killRepeater()
{

    //copying string data to char array
    this.inputStr.getChars(0 , this.inputStr.length() , catchStr , 0);

    //------------------

    for(int counter = 0 ; counter < this.inputStr.length() ; counter++)
    {
        if(catchStr[counter] != catchStr[counter - 1])
        {
            modifiedStr = modifiedStr + catchStr[counter];
        }
    }

    return modifiedStr;
}

}

Here is Output when killRepeater() is called.

java.lang.ArrayIndexOutOfBoundsException: src.length=5 srcPos=0 dst.length=1 dstPos=0 length=4

at java.lang.System.arraycopy(Native Method)
at java.lang.String.getChars(String.java:894)   
at doubleKiller.killRepeater(Main.java:23)
    at useThings.main(Main.java:49) 
at java.lang.reflect.Method.invokeNative(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:515) 
at com.aide.ui.build.java.RunJavaActivity$1.run(SourceFile:108) 
at java.lang.Thread.run(Thread.java:862)

Tell me my error...Thanks in advance

Answer 1

You are doing

private String inputStr = " "; 
private char[] catchStr = new char[inputStr.length()];

inputStr.length() returns 1 , that is, the size from the string " ", so, you have a char array with size 1 .

When you do:

for(int counter = 0 ; counter < this.inputStr.length() ; counter++){
    if(catchStr[counter] != catchStr[counter - 1]){

With a inputStr.length() > 1 you have an ArrayIndexOutOfBoundsException .

Also, when run catchStr[counter - 1]) for the first time, counter-1 would generate -1 , which isn't a valid index . Try running the counter from 1 to avoid this error.

Declare your array with a fixed size (eg 200) or use an ArrayList . You could also put catchStr = new char[inputStr.length()] after taking the input of the String.

Answer 2

Good thing that you asking about specific problem, but in case you interested how to make this simpler, there is regex magic

String in = "ballooooon";
String out = in.replaceAll("(.)\\1+", "$1"); // balon

Which means

find any symbol, save it to group 1, if next symbol, or symbols are equal to group 1, delete them and leave just one from the group.

Answer 3

You are initializing catchStr with inputStr.length(). But at this time inputStr = " ". So catchStr has a length of 1. When you later populate inputStr to a bigger value, you try and copy that into a char[] of length 1 and it doesn't fit. Add catchStr = new char[inputStr.length()]; right before you do the copy.

Answer 4

When you initialise catchStr it will always have the value of 1, because inputStr is " " and therefore it's length is 1.

private String inputStr = " ";
private char[] catchStr = new char[inputStr.length()];

When you loop on counter in the method killRepeater() you will get an ArrayOutOfBoundsException because the string you pass in getString is probably greater than 1.

---

Consider moving new char[inputStr.length()] into getString .

public void getString(String inputStr) {
    this.inputStr = inputStr;
    this.catchStr = new char[inputStr.length()];
}

And, setting the attribute catchStr to uninitialised.

private char[] catchStr;

---

The second issue is with your for loop. You start the counter at 0 and use catchStr[counter - 1] to look back on the previous character. This will not work when counter = 0 because the index will evaluate to -1.

Consider starting your counter at 1, and continue to work on the method from there. You'll need to tweak it a little to get it output the desired string.

for (int counter = 1; counter < this.inputStr.length(); counter++) {
    if (catchStr[counter] != catchStr[counter - 1]) {
        modifiedStr = modifiedStr + catchStr[counter];
    }
}