patternjavaModerate
Usage of StringBuilder for returning copies of a string
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copiesusagereturningforstringbuilderstring
Problem
Given a string and a non-negative int n, we'll say that the front of the string is the first 3 chars, or whatever is there if the string is less than length 3. Return n copies of the front:
I've solved above problem using following code but I'm using a new
frontTimes("Chocolate", 2) → "ChoCho"
frontTimes("Chocolate", 3) → "ChoChoCho"
frontTimes("Abc", 3) → "AbcAbcAbc"
frontTimes("X", 3) → "XXX"I've solved above problem using following code but I'm using a new
StringBuilder to store intermediate string result. Does it really needed can I optimize and remove the for loop in the else?public String frontTimes(String str, int n) {
StringBuilder sb = new StringBuilder(str);
StringBuilder newsb = new StringBuilder();
if(sb.length() >= 3)
{
for(int i = 0; i < n; i++)
{
newsb.append(sb.substring(0,3));
}
return newsb.toString();
}
else
{
for(int i = 0; i < n; i++)
{
newsb.append(sb.toString());
}
return newsb.toString();
}
}Solution
I'd just like to make a slight change to the code. When you are instantiating a
Note how many times that 3 is declared? Would be better to extract that to a constant, or even better, a parameter. And with a few other changes to the above (as suggested by @rolfl in chat):
StringBuilder, you have the opportunity to specify the capacity of it. Using this constructor, we can avoid having it resized more than necessary.public String frontTimes(String str, int n) {
StringBuilder stringBuilder = new StringBuilder(3 * n);
if (str.length() > 3) {
str = str.substring(0, 3);
}
for (int i = 0; i < n; i++) {
stringBuilder.append(str);
}
return stringBuilder.toString();
}Note how many times that 3 is declared? Would be better to extract that to a constant, or even better, a parameter. And with a few other changes to the above (as suggested by @rolfl in chat):
public String frontTimes(final String str, final int frontLength, final int times) {
String copyString = str.length() > frontLength ? str.substring(0, frontLength) : str;
StringBuilder stringBuilder = new StringBuilder(copyString.length() * times);
for (int i = 0; i < times; i++) {
stringBuilder.append(copyString);
}
return stringBuilder.toString();
}Code Snippets
public String frontTimes(String str, int n) {
StringBuilder stringBuilder = new StringBuilder(3 * n);
if (str.length() > 3) {
str = str.substring(0, 3);
}
for (int i = 0; i < n; i++) {
stringBuilder.append(str);
}
return stringBuilder.toString();
}public String frontTimes(final String str, final int frontLength, final int times) {
String copyString = str.length() > frontLength ? str.substring(0, frontLength) : str;
StringBuilder stringBuilder = new StringBuilder(copyString.length() * times);
for (int i = 0; i < times; i++) {
stringBuilder.append(copyString);
}
return stringBuilder.toString();
}Context
StackExchange Code Review Q#78761, answer score: 13
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