In Java, we can use the String’s extension method startsWith to check if it starts with a prefix. We can even specify the start position for the string matching comparison.
Have you wondered how these methods are implemented in JDK? See below:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 | public class StringUtils { public boolean startsWith(String prefix, int toffset) { startsWith(prefix, 0); } public boolean startsWith(String prefix, int toffset) { char ta[] = value; var to = toffset; char pa[] = prefix.value; int po = 0; var pc = prefix.value.length; if ((toffset < 0) || (toffset > value.length - pc)) { return false; } while (--pc >= 0) { if (ta[to++] != pa[po++]) { return false; } } return true; } } |
public class StringUtils {
public boolean startsWith(String prefix, int toffset) {
startsWith(prefix, 0);
}
public boolean startsWith(String prefix, int toffset) {
char ta[] = value;
var to = toffset;
char pa[] = prefix.value;
int po = 0;
var pc = prefix.value.length;
if ((toffset < 0) || (toffset > value.length - pc)) {
return false;
}
while (--pc >= 0) {
if (ta[to++] != pa[po++]) {
return false;
}
}
return true;
}
}No tricks are used – simply comparing character by character for the prefix and the string to see if both matches. The time complexity is O(N) where N is the number of characters in prefix.
–EOF (The Ultimate Computing & Technology Blog) —
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