I was recently asked this question in an interview(3+ experience). No String function allowed including String.length. I was given 5 minutes to write the complete code.
Example
String ="abcfedbca"
subString = "fed"
Actually i asked him to elaborate a little more to which he said "it's easy java implementation what should i elaborate" and on basis of this question only he said my core java is very weak.
Note that you're question is not very precise and hence your requirements are not very clear.
Simple way :
String st = new StringBuilder(s).substring(3,6);
Or you can directly construct the new String using reflection to get the char array:
public static String substring(String s, int from, int to){
Field f = String.class.getDeclaredField("value");
f.setAccessible(true);
char [] tab = (char[])f.get(s);
f.setAccessible(false);
return new String(tab, from, to - from);
}
String fits an hexadecimal format) :
String s ="abcfedbca";
BigInteger bi = new BigInteger(s, 16);
bi = bi.and(new BigInteger("16699392")); //0xfed000 in hexa
bi = bi.shiftRight(12);
System.out.println(bi.toString(16));
Or more simple :
String s ="abcfedbca";
System.out.println(Integer.toHexString((int)(Long.parseLong(s, 16) & 16699392) >> 12));
If you want a more general method, this one might suits your case :
public static void main(String [] args){
String s ="abcfedbca";
System.out.println(substring(s, 2, 5, 9));
}
public static String substring (String s, int from, int to, int length){
long shiftLeft = 0;
long shiftRight = (length - to - 1) * 4;
for(int i = 0; i < to - from - 1; i++){
shiftLeft += 15;
shiftLeft = shiftLeft << 4;
}
shiftLeft += 15;
return Long.toHexString((Long.parseLong(s, 16) & (shiftLeft << shiftRight)) >> shiftRight);
}
StringBuffer will use them, that's why I said the requirements were not very clear).
StringBuilder is the way to go.StringBuilder ?You can use a StringBuilder and call substring on it. Don't know whether that'd be allowed.
Here is the other way (although I am ashamed of this solution):
String str = "abcfedbca";
int from = 3, length = 3;
java.lang.reflect.Field valueField = String.class.getDeclaredField("value");
valueField.setAccessible(true);
char[] value = (char[]) valueField.get(str);
char[] sub = new char[length];
System.arraycopy(value, from, sub, 0, length);
String substring = new String(sub);
String buff = "abcfedbca";
System.out.println("substring is = " + buff.substring(3, 6));
how about this?
StringBuffer constructor with a String parameter call super(str.length() + 16);StringBuilder seems like a cheat to me since it's based on strings. I'd argue that you have to go down to byte primitives to meet the spirit of the test. Of course this calls getBytes which is technically a String function, so that breaks it also.
public static void main(String[] args) {
String full ="abcfedbca";
String desiredsubString = "fed";
byte[] fullByte = full.getBytes();
byte[] desiredByte = desiredsubString.getBytes();
byte[] foundStorage = new byte[desiredByte.length];
boolean foundStart = false;
int inserted = 0;
for (byte b : fullByte) {
if ( !foundStart && (b == desiredByte[0]) )
{
foundStorage[0] = b;
inserted++;
foundStart = true;
}
else if (foundStart && (inserted < foundStorage.length))
{
foundStorage[inserted] = b;
inserted++;
if ( inserted >= foundStorage.length )
{
break;
}
}
}
System.out.println("These should be equal: " + new String(desiredByte).equals(new String(foundStorage)));
}
String.getBytes can be considered a "string method".Maybe:
String value = "abcfedbca";
BigInteger bi = new BigInteger(value, 16);
bi = bi.divide(BigInteger.TEN);
bi = bi.divide(BigInteger.TEN);
bi = bi.divide(BigInteger.TEN);
bi = bi.divide(BigInteger.TEN);
bi = bi.divide(BigInteger.TEN);
bi = bi.divide(BigInteger.TEN);
bi = bi.divide(BigInteger.TEN);
int val = bi.subtract(BigInteger.valueOf(535)).intValue();
String hex = Integer.toHexString(val);
System.out.println(hex);
Output: fed
How about using a JPasswordField to get the chars:
private static String substring(String str, int beginIndex, int endIndex) {
return new String(new JPasswordField(str).getPassword(), beginIndex, endIndex - beginIndex);
}
And the String constructor is not a String method, isn't it?
public String submethod(String data, int firstindex, int lastindex) {
char[] chars=data.toCharArray();
char[]charnew= new char [lastindex];
for(int i=firstindex; i< lastindex;i++) {
charnew[i]=chars[i];
}
return new String(charnew);
}
public String subString(String str, int i, int j) { p = Runtime.getRuntime().exec("echo " + str + "| cut -c"+i+"-"+j); p.waitFor(); return new BufferedReader(new InputStreamReader(p.getInputStream())).readLine();}(*NIX only)