Reverse a string in Java
Reverse a string in Java
Question
I have "Hello World" kept in a String variable named hi.
I need to print it, but reversed.
How can I do this? I understand there is some kind of a function already built-in into Java that does that.
Related: Reverse each individual word of “Hello World” string with Java
Accepted Answer
You can use this:
new StringBuilder(hi).reverse().toString()
Or, for versions earlier than JDK 1.5, use java.util.StringBuffer instead of StringBuilder — they have the same API. Thanks commentators for pointing out that StringBuilder is preferred nowadays when there is no concurrency concern.
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For Online Judges problems that does not allow StringBuilder or StringBuffer, you can do it in place using char[] as following:
public static String reverse(String input){
char[] in = input.toCharArray();
int begin=0;
int end=in.length-1;
char temp;
while(end>begin){
temp = in[begin];
in[begin]=in[end];
in[end] = temp;
end--;
begin++;
}
return new String(in);
}
public static String reverseIt(String source) {
int i, len = source.length();
StringBuilder dest = new StringBuilder(len);
for (i = (len - 1); i >= 0; i--){
dest.append(source.charAt(i));
}
return dest.toString();
}
http://www.java2s.com/Code/Java/Language-Basics/ReverseStringTest.htm
String string="whatever";
String reverse = new StringBuffer(string).reverse().toString();
System.out.println(reverse);
I am doing this by using the following two ways:
Reverse string by CHARACTERS:
public static void main(String[] args) {
// Using traditional approach
String result="";
for(int i=string.length()-1; i>=0; i--) {
result = result + string.charAt(i);
}
System.out.println(result);
// Using StringBuffer class
StringBuffer buffer = new StringBuffer(string);
System.out.println(buffer.reverse());
}
Reverse string by WORDS:
public static void reverseStringByWords(String string) {
StringBuilder stringBuilder = new StringBuilder();
String[] words = string.split(" ");
for (int j = words.length-1; j >= 0; j--) {
stringBuilder.append(words[j]).append(' ');
}
System.out.println("Reverse words: " + stringBuilder);
}
Take a look at the Java 6 API under StringBuffer
String s = "sample";
String result = new StringBuffer(s).reverse().toString();