Can I multiply strings in Java to repeat sequences?
JavaStringJava Problem Overview
I have something like the following:
int i = 3;
String someNum = "123";
I'd like to append i
"0"s to the someNum
string. Does it have some way I can multiply a string to repeat it like Python does?
So I could just go:
someNum = sumNum + ("0" * 3);
or something similar?
Where, in this case, my final result would be:
"123000".
Java Solutions
Solution 1 - Java
The easiest way in plain Java with no dependencies is the following one-liner:
new String(new char[generation]).replace("\0", "-")
Replace generation with number of repetitions, and the "-" with the string (or char) you want repeated.
All this does is create an empty string containing n number of 0x00 characters, and the built-in String#replace method does the rest.
Here's a sample to copy and paste:
public static String repeat(int count, String with) {
return new String(new char[count]).replace("\0", with);
}
public static String repeat(int count) {
return repeat(count, " ");
}
public static void main(String[] args) {
for (int n = 0; n < 10; n++) {
System.out.println(repeat(n) + " Hello");
}
for (int n = 0; n < 10; n++) {
System.out.println(repeat(n, ":-) ") + " Hello");
}
}
Solution 2 - Java
No, but you can in Scala! (And then compile that and run it using any Java implementation!!!!)
Now, if you want to do it the easy way in java, use the Apache commons-lang package. Assuming you're using maven, add this dependency to your pom.xml:
<dependency>
<groupId>commons-lang</groupId>
<artifactId>commons-lang</artifactId>
<version>2.4</version>
</dependency>
And then use StringUtils.repeat as follows:
import org.apache.commons.lang.StringUtils
...
someNum = sumNum + StringUtils.repeat("0", 3);
Solution 3 - Java
String::repeat
Use String::repeat
in Java 11 and later.
Examples
"A".repeat( 3 )
>AAA
And the example from the Question.
int i = 3; //frequency to repeat
String someNum = "123"; // initial string
String ch = "0"; // character to append
someNum = someNum + ch.repeat(i); // formulation of the string
System.out.println(someNum); // would result in output -- "123000"
Solution 4 - Java
Google Guava provides another way to do this with Strings#repeat()
:
String repeated = Strings.repeat("pete and re", 42);
Solution 5 - Java
Two ways comes to mind:
int i = 3;
String someNum = "123";
// Way 1:
char[] zeroes1 = new char[i];
Arrays.fill(zeroes1, '0');
String newNum1 = someNum + new String(zeroes1);
System.out.println(newNum1); // 123000
// Way 2:
String zeroes2 = String.format("%0" + i + "d", 0);
String newNum2 = someNum + zeroes2;
System.out.println(newNum2); // 123000
Way 2 can be shortened to:
someNum += String.format("%0" + i + "d", 0);
System.out.println(someNum); // 123000
More about String#format()
is available in its API doc and the one of java.util.Formatter
.
Solution 6 - Java
If you're repeating single characters like the OP, and the maximum number of repeats is not too high, then you could use a simple substring operation like this:
int i = 3;
String someNum = "123";
someNum += "00000000000000000000".substring(0, i);
Solution 7 - Java
No. Java does not have this feature. You'd have to create your String using a StringBuilder, and a loop of some sort.
Solution 8 - Java
Simple way of doing this.
private String repeatString(String s,int count){
StringBuilder r = new StringBuilder();
for (int i = 0; i < count; i++) {
r.append(s);
}
return r.toString();
}
Solution 9 - Java
Java 8 provides a way (albeit a little clunky). As a method:
public static String repeat(String s, int n) {
return Stream.generate(() -> s).limit(n).collect(Collectors.joining(""));
}
or less efficient, but nicer looking IMHO:
public static String repeat(String s, int n) {
return Stream.generate(() -> s).limit(n).reduce((a, b) -> a + b);
}
Solution 10 - Java
I created a method that do the same thing you want, feel free to try this:
public String repeat(String s, int count) {
return count > 0 ? s + repeat(s, --count) : "";
}
Solution 11 - Java
with Dollar:
String s = "123" + $("0").repeat(3); // 123000
Solution 12 - Java
I don't believe Java natively provides this feature, although it would be nice. I write Perl code occasionally and the x
operator in Perl comes in really handy for repeating strings!
However StringUtils
in commons-lang
provides this feature. The method is called repeat()
. Your only other option is to build it manually using a loop.
Solution 13 - Java
With Guava:
Joiner.on("").join(Collections.nCopies(i, someNum));
Solution 14 - Java
No, you can't. However you can use this function to repeat a character.
public String repeat(char c, int times){
StringBuffer b = new StringBuffer();
for(int i=0;i < times;i++){
b.append(c);
}
return b.toString();
}
Disclaimer: I typed it here. Might have mistakes.
Solution 15 - Java
A generalisation of Dave Hartnoll's answer (I am mainly taking the concept ad absurdum, maybe don't use that in anything where you need speed). This allows one to fill the String up with i characters following a given pattern.
int i = 3;
String someNum = "123";
String pattern = "789";
someNum += "00000000000000000000".replaceAll("0",pattern).substring(0, i);
If you don't need a pattern but just any single character you can use that (it's a tad faster):
int i = 3;
String someNum = "123";
char c = "7";
someNum += "00000000000000000000".replaceAll("0",c).substring(0, i);
Solution 16 - Java
Similar to what has already been said:
public String multStuff(String first, String toAdd, int amount) {
String append = "";
for (int i = 1; i <= amount; i++) {
append += toAdd;
}
return first + append;
}
Input multStuff("123", "0", 3);
Output "123000"
Solution 17 - Java
we can create multiply strings using * in python but not in java you can use for loop in your case:
String sample="123";
for(int i=0;i<3;i++)
{
sample=+"0";
}
Solution 18 - Java
There's no shortcut for doing this in Java like the example you gave in Python.
You'd have to do this:
for (;i > 0; i--) {
somenum = somenum + "0";
}
Solution 19 - Java
The simplest way is:
String someNum = "123000";
System.out.println(someNum);