Below is the syntax highlighted version of Permutations.java from §2.3 Recursion.

/******************************************************************************
 * Compilation: javac Permutations.java
 * Execution: java Permutations n
 *
 * Enumerates all permutations on n elements.
 * Two different approaches are included.
 *
 * % java Permutations 3
 * abc
 * acb
 * bac
 * bca
 * cab
 * cba
 *
 ******************************************************************************/
publicclassPermutations{
// print n! permutation of the characters of the string s (in order)
publicstaticvoidperm1(String s){perm1("", s);}
privatestaticvoidperm1(String prefix,String s){
int n = s.length();
if(n ==0) StdOut.println(prefix);
else{
for(int i =0; i < n; i++)
perm1(prefix + s.charAt(i), s.substring(0, i)+ s.substring(i+1, n));
}
}
// print n! permutation of the elements of array a (not in order)
publicstaticvoidperm2(String s){
int n = s.length();
char[] a =newchar[n];
for(int i =0; i < n; i++)
 a[i]= s.charAt(i);
perm2(a, n);
}
privatestaticvoidperm2(char[] a,int n){
if(n ==1){
 StdOut.println(newString(a));
return;
}
for(int i =0; i < n; i++){
swap(a, i, n-1);
perm2(a, n-1);
swap(a, i, n-1);
}
}
// swap the characters at indices i and j
privatestaticvoidswap(char[] a,int i,int j){
char c = a[i];
 a[i]= a[j];
 a[j]= c;
}
publicstaticvoidmain(String[] args){
int n = Integer.parseInt(args[0]);
String alphabet ="abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
String elements = alphabet.substring(0, n);
perm1(elements);
 StdOut.println();
perm2(elements);
}
}