java array of problems , thank

public class Example {
String str = new String ("good");
char [] ch = {'a', 'b', 'c'};
public static void main (String args []) {
Example ex = new Example ();
ex.change (ex.str, ex.ch);
System.out.print (ex.str + "and");
System.out.print (ex.ch);
}

public void change (String str, char ch []) {
str = "test ok";
ch [0] = 'g';
}
}
Output : good and gbc

this small program , the change process char [] array ch Why not this.ch [0] = 'g'; at a time when output has changed ?
------ Solution ---------------------------------------- ----
arrays are passed by reference
------ For reference only --------------------------- ------------


Thank you !
passed by reference : that is passed before and after passing a reference point to the same