How to do the opposite of StringBuilder append in Java?

Question

What would be the opposite of:

savedPlanets.append(planet.getDisplayName()+",");

I have a list and I am adding the name of the planet every time the user clicks on a checkbox, I want to remove the name from the savedPlanets if the checkbox is cleared

remove. the beauty is you get to declare what you want it to be.. maybe destroyPlanet() :) — Randy, Sep 10 '12 at 14:04
savedPlanets is a String. How would I implement a set of data? — fasheikh, Sep 10 '12 at 14:05
if savedPlanet is a string, just replace it with empty string — hndr, Sep 10 '12 at 14:05
@Randy how could I implement that? I can't empty the String as I need the other values — fasheikh, Sep 10 '12 at 14:06
make a new class Planets. create methods for addPlanet, RemovePlanet.. etc. also include toString() to get the string you are trying to create here. — Randy, Sep 10 '12 at 14:08
Single character subset: http://stackoverflow.com/questions/3395286/remove-last-character-of-a-stringbuilder — Ciro Santilli OurBigBook.com, Mar 23 '15 at 11:33

Bharat Sinha · Accepted Answer · 2012-09-10T14:12:54.327

3

You can do following:

 savedPlanets.replace(planet.getDisplayName(),"");

Ideally I would do a solution like following:

Set<String> selectedPlanets = new HashSet<String>();

selectedPlanets.add(planet.getDisplayName());        // Whenever a planet is selected
selectedPlanets.remove(planet.getDisplayName());     // Whenever a planet is removed 

// Prepare a String with all planets        
StringBuilder savedPlanets = new StringBuilder("");
for(String planetName : selectedPlanets ){
    savedPlanets.append(planetName).append(",");
}
// Removing , from the end if any       
if(savedPlanets.toString().endsWith(","))
    finalValue = savedPlanets.substring(0, savedPlanets.length()-1);

// finalValue is what you are looking for

edited Sep 10 '12 at 14:12

answered Sep 10 '12 at 14:06

Bharat Sinha

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1

nice thought. but really this wants to be a map or set of some sort. then the string is a toString function return value. – Randy Sep 10 '12 at 14:07
Rather than building the string yourself, I would use a String/Collection utility library (Guava's Joiner or Commons StringUtils) which take a similar approach but don't duplicate the String object with use of substring and are flexible in the separator that is used (read: higher reuse) – Tom Hartwell Jul 03 '14 at 16:48

score 1 · Answer 2 · answered Sep 10 '12 at 14:07

1

I would rebuilt the string each time, only including the element you want to include.

e.g.

Set<Planet> planets = ...
StringBuilder sb = new StringBuilder();
String sep = "";
for(Planet planet: planets) {
   sb.append(sep).append(planet.getDisplayName());
   sep = ",";
}
String planetNames = sb.toString();

answered Sep 10 '12 at 14:07

Peter Lawrey

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2

Nice approach. Apache Commons StringUtils is flexible and handles this nicely, as does Guava's Joiner library. I would lean towards using those in a project of any size. For example, StringUtils optimizes the StringBuilder initial size and handles nulls gracefully. – Tom Hartwell Jul 03 '14 at 16:52

score 0 · Answer 3 · answered Sep 10 '12 at 14:05

I think you're using StringBuffer or something like that. It's not a good solution it this case, I would recommend you to use Set. http://docs.oracle.com/javase/6/docs/api/java/util/Set.html

Implement it like this:

Set planets = new HashSet();
planets.add("a");
planets.add("b");
planets.remove("a");

MAC · Answer 4 · 2012-09-10T14:13:43.770

Assume... StringBuffer savedPlanets...

APPEND : savedPlanets.append(planet.getDisplayName()+",");

OPPOSITE OF APPEND : savedPlanets.replaceAll(planet.getDisplayName()+",","");

EX:

savedPlanets.append("Earth,");
savedPlanets.append("Mercury,");
savedPlanets.append("Venus,");

now savedPlanetes= "Earth,Mercury,Venus,";

then

savedPlanets.replaceAll("Venus,",""); <-----

now value will be savedPlanetes= "Earth,Mercury,";

How to do the opposite of StringBuilder append in Java?

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