Pass parameter to method

Question

import java.util.*;
public class Test {
/** Creates a new instance of Test */
public Test() {
StringBuffer a = new StringBuffer("A");
StringBuffer b = new StringBuffer("B");
operate(a,b);
System.out.print(a+" "+b);
public void operate(StringBuffer a, StringBuffer b)
a.append(b);
b=a;
public static void main(String[] args){
Test t = new Test();
I known in Java, when you pass an object to method, it will be pass -by - reference, but when i run this program, the output is a="AB", b="B", it's not a=b="AB" i guest. Who know the reason, please help me. ?
This is the case simlilar to:
public class TestInteger {
/** Creates a new instance of TestInteger */
public TestInteger() {
public static void add3(Integer i){
int v = i.intValue();
v +=3;
i = new Integer(v);
public static void main(String[] args){
Integer i = new Integer(0);
add3(i);
System.out.print(i.intValue());
The output is 0 not 3

Answer 1

The below code snippets should take care of the issue for both the StringBuffer and the Integer issues. I tend to retun the object that you want to pass around:
public class Test {
public Test() {
StringBuffer a = new StringBuffer("A");
StringBuffer b = new StringBuffer("B");
StringBuffer c = new StringBuffer();
c = operate(a,b);
//System.out.print(a+" "+b);
System.out.print(c+" "+c);
public StringBuffer operate(StringBuffer a, StringBuffer b)
a.append(b);
return b=a;
public static void main(String[] args){
Test t = new Test();
public class Test {
public Test() {
public static Integer add3(Integer i){
int v = i.intValue();
v +=3;
return new Integer(v);
public static void main(String[] args){
Integer i = new Integer(0);
i = add3(i);
System.out.print(i.intValue());
}