Manipulating Strings on Arrays

I am assuming that by "array of strings" you mean:

String[] myvariable = new String[number];
myvariable[0] = "ABBCCBBAA";
myvariable[1] = "some_other_string";

If you are new to Java I suggest you read a beginner's book like Head First Java and also look into java documentation; you don't even have to go that far if you are programming with a decent IDE, like Netbeans (thanks to its intelli-sense feature) is a source of documentation for what you seek (meaning that you can look at all the methods available for a string, read what they do, and see if they can help accomplish what you need).

I am assuming (from what you have said) that you want to replace "AA" for "A", and from that result replace "BB" for "BA", and from that result replace "AB" into "CC", and from that result "BC" into "B".

The code I am posting is REAL simple, and it will only work for this particular case (as I have understood it), if you want to create a method that does this for any string, you need to change some things, but I'll leave that to you.

String[] yourArrayOfStrings = new String[1];
yourArrayOfStrings[0] = "ABBCCBBAA";

String resultOfReplacement= yourArrayOfStrings[0].replaceFirst("AA", "A");
System.out.println(resultOfReplacement); //debugging purposes

resultOfReplacement = resultOfReplacement.replaceFirst("BB", "BA");
System.out.println(resultOfReplacement); //debugging purposes

resultOfReplacement = resultOfReplacement.replaceFirst("AB", "CC");
System.out.println(resultOfReplacement); //debugging purposes

resultOfReplacement = resultOfReplacement.replaceFirst("BC", "BB");
System.out.println(resultOfReplacement); //debugging purposes

The only reason why I created a String[] was because that's what you stated in your question, otherwise I would have simple created a String variable like I did with resultOfReplacement. To access the first element in an array you do arrayVariable[index]. Here I use the replaceFirst function that comes with Java for variables of type String. If you look the method up, it'll tell you that it will look for the first match of the first parameter and replace it with the second parameter.

The System.out.println I have added are for debugging purposes, so you can see on the console what is clearly happening with each replacement. So, the first time I call replaceFirst(...) on the original string which is a[0].

This will happen:

The method will look in "ABBCCBBAA" for the FIRST AND ONLY THE FIRST time "AA" appears and replace it with "A". The result is "return" and you must assign it to a variable if you want access to it to do more actions upon it. In this case, I assign it to a new String variable. You could have just assigned back to a[0], which is likely what you want. (You'd do so like this: a[0]=ourArrayOfStrings[0].replaceFirst("AA", "A");)

For the second replacement, the method will look in "ABBCCBBA" for the first time "BB" appears and replace it for "BA".

See the pattern? This is just a start, and depending on what you want you might need other methods like replaceAll().

Most IDEs will tell you what methods are available for a variable when you access it via ".", so that when you are typing " variablename. " right at that moment a list of methods available for it should appear, if they don´t you can go ahead and do a shortcut like ctrl+space for it to appear and navigate through the methods via the arrow keys so you can read what they do (at least for Eclpise and Netbeans, while programming in Java, it works). Documentation is power!