根据Java中另一个数组中的值初始化一个数组

Question

what's wrong with this code? I want to insert in array cnew as- if carr contains 'a' cnew should get 100(int), for 't'- cnew should get 101(int), for 'g'-110 and for 'c'-111.

String s="atgc";
len=s.length();

char[] carr=s.toCharArray();
char[] cnew = new char[len];

for(int i=0;i<len;i++){
    for(int j=0;j<len;j++){
    if(carr[j]=='a'){
        cnew[i]=100;
    }else if(carr[j]=='t'){
        cnew[i]=101;
    }else if(carr[j]=='g'){
        cnew[i]=110;
    }else
        cnew[i]=111;


    }
}

Answer 1

There's no need for a nested loop :

    String s="atgc"; 
    int len=s.length();
    char[] carr = s.toCharArray(); 
    int[] cnew = new int[len];
    for(int i=0;i<len;i++) {
      if (carr[i]=='a'){
        cnew[i]=100;
      } else if(carr[i]=='t') {
        cnew[i]=101;
      } else if(carr[i]=='g') {
        cnew[i]=110;
      } else {
        cnew[i]=111;
      }
    }

Produces the following array :

[100, 101, 110, 111]

If you want cnew to contain int values, make it an int array.

Answer 2

There is no need to nested loop, because of it you are doing same operation twice. Both arrays are same length, so they could use one index.

I could also propose shorter version, with Map:

String s="atgc";

char[] carr=s.toCharArray();
char[] cnew = new char[carr.length];
Map<Character, Integer> mapping = new HashMap<Character, Integer>();
mapping.put('t',101);
mapping.put('a',100);
mapping.put('g',110);// this solution would be better for more letter mappings

for(int i=0;i<len;i++){
   if(mapping.containsKey(carr[i])) {
     cnew[i]=mapping.get(carr[i]);
   } else {
     cnew[i]=111;
   }
}