CODEWITHSUNDEEP
javastring
QWERTY
QWERTY

Reputation: 2315

Java how to replace last character of string to specific character

I was having some problem when trying to format the string. So basically I got enqueue and dequeue and it was working fine now. Here is the code:

public String toString(){
    String str = "[";
    for(int i = front; i<= rear; i++){
        str += Q[i] + ",";  
    }

    if(str.length() > 0 && str.charAt(str.length()-1)==','){
        str.substring(0, str.length()-1);
    }

    return str;
}

I wanted the result to be like [1,2,3,4]. However, I have no idea how to replace the last "," to "]". The current problem is it returns me [1,2,3,4, and that's it.

Upvotes: 1

Views: 136

Answers (6)

zrvan
zrvan

Reputation: 7743

There is the new, Java 8 only style:

Arrays.stream(Arrays.copyOfRange(Q, front, rear)).collect(Collectors.joining(",", "[", "]");

Which implicitly creates a StringJoiner with the parameters passed to Collectors.joining(), delimiter, prefix, suffix. While not specifically answering your question as it is phrased, it solves the actual problem you're facing.

Upvotes: 0

Pshemo
Pshemo

Reputation: 124215

First of all, don't use concatenation += inside loops 

for (...){
    //...
    resultString += newString
    //...
}

to create string result. This way each time you execute this code it creates new String which needs to copy value from resultString and add newString.

Instead use proper tools like StringBuilder and its append method. This prevents copying previous result each time (which can take some time) and places newString in bigger buffer. So make your code more like

StringBuilder sb = new StringBuilder();
for (...){
    sb.append(newString);
}
String result = sb.toString();

Also if you want to add delimiter like , you can use new StringJoiner(delimiter) (added in Java 8) or if you want to add prefix and suffix like [ and ] use new StringJoinder(delimiter, prefix, suffix).

So your code can look more or less like:

StringJoiner sj = new StringJoiner(",", "[", "]");
for(int i = front; i<= rear; i++){
   sj.add(Q[i]);  
}
return sj.toString();

or even

return IntStream
       .rangeClosed(fron, rear)
       .mapToObj(i->Q[i])
       .collect(Collectors.joining(",", "[", "]"));

Upvotes: 1

Eran
Eran

Reputation: 393771

How about :

String str = "[";
for(int i = front; i< rear; i++){
    str += Q[i] + ",";  
}
str += Q[rear] + "]";

Of course, I'd use StringBuilder instead of String concatenation :

StringBuilder str = new StringBuilder(128);
str.append('[');
for(int i = front; i< rear; i++){
    str.append(Q[i]);
    str.append(',');  
}
if (rear > front) {
    str.append(Q[rear]);
}
str.append(']'); 
return str.toString();

Upvotes: 1

MathiasCiarlo
MathiasCiarlo

Reputation: 300

public String toString(){
    String str = "[";
    for(int i = front; i<= rear; i++){
        if (i == rear)
            str += Q[i] + ","; 
        else
            str += Q[i] + "]";
    }

    return str;
}

Upvotes: 1

Lrrr
Lrrr

Reputation: 4817

change : 

for(int i = front; i<= rear; i++){
    str += Q[i] + ",";  
}

to : 

for(int i = front; i< rear; i++){
    str += Q[i] + ",";  
}
str+=Q[rear] + "]";

also it is better to use StringBuilder.append() instead of str +=, Because String is immutable and every time you use str+= it creates new instance of your str Object

with StringBuilder it will be : 

StringBuilder str = new StringBuilder();
str.append("[");
for(int i = front; i<= rear; i++){
    str.append(Q[i] + ",");  
}
str.append(Q[rear] + "]");

Upvotes: 3

Avinash Raj
Avinash Raj

Reputation: 174696

Use string.replaceAll

string.replaceAll(",(?=[^,]*$)", "]");

OR

string.replaceAll("(?m),$", "]");

Upvotes: 1

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