java值传递

public static void main(String[] args) {  
    String x = new String("ab");  
    change(x);  
    System.out.println(x);  
}  
   
public static void change(String x) {  
    x = "cd";  
}  

public static void main(String[] args) {  
    StringBuilder x = new StringBuilder("ab");  
    change(x);  
    System.out.println(x);  
}  
   
public static void change(StringBuilder x) {  
    x.delete(0, 2).append("cd");  
}