javase-為何輸出結果是good gbc 10只有數組改變了？？？？

為何輸出結果是good gbc 10只有數組改變了？？？？

public class Aed {
String str = new String("good");
char[] ch = {'a','b','c'};
int num = 10;

public void change(String str,char[] ch,int num){
    str = "test ok";
    ch[0] = 'g';
    num = 20;
}

public static void main(String[] args) {
    Aed a = new Aed();
    a.change(a.str,a.ch, a.num);
    System.out.print(a.str);
    System.out.print(a.ch);
    System.out.print(a.num);
}

}

最佳回答：

     public void change(String str,char[] ch,int num){
            str = "test ok";
            ch[0] = 'g';
            num = 20;
    }


    改為

        public void change(String str,char[] ch,int num){
            this.str = "test ok";
            this.ch[0] = 'g';
            this.num = 20;
    }