A brief analysis of Java method transfer value and reference

public class Test { 
    public static void stringUpd(String str) { 
        str = str.replace("j", "l"); 
        System.out.println(str); 
    }    
    public static void stringBufferUpd(StringBuffer bf) { 
        bf.append("c"); 
        System.out.println(bf); 
    }    
    public static void main(String[] args) { 

         
        String s1 = new String("java"); 
        stringUpd(s1); 
        System.out.println(s1); 

          

         
        StringBuffer bb = new StringBuffer("java"); 
        stringBufferUpd(bb); 
        System.out.println(bb); 

    } 

}