How to find error of this program

Question

public class Main{
public static void main (String[] args)
{
//find the length
String name="sam";
String name2="ram";
System.out.println(name.length());

//find the position element
System.out.println(name.charAt(0));

//concatenate the string
String name3=name+" and "+name2;
System.out.println(name3);

//replace the letter
String name4=name.replace(oldchar:'a',newchar:'1');
System.out.println(name4);

}
}

Answer 1

By compiling!!!!!!!!!!!!

No need to specify oldchar, newchar like that..
just write like :
name.replace('a', '1') ;