Input
System.out.println(9);
int a=1;
int b=10;
System.out.println(b);
int c=a+b;
System.out.println(c);
Output
out.println(9);
int a=1;
int b=10;
out.println(b);
int c=a+b;
out.println(c);
Match at the beginning and replacement
package egtry.regex;
public class EachlineMatch {
public static void main(String[] args) {
String text="System.out.println(9);\nint a=1;\nint b=10;\nSystem.out.println(b);\nint c=a+b;\n System.out.println(c);\n";
String newString=text.replaceAll("(?m)^\\s*System\\.out", "out");
System.out.println(newString);
}
}