I still don't understand the object reference

阿迪雅

class Base
{
public int i;
public Base (int a)
{
i = a;
}
}

public class StringTest {
  public static void changeStr (String str) {
    str = "welcome";
  }
  public static void changeBase (Base b)
  {
  b.i = 6;
  }
  
  public static void main (String [] args) {
    String str = "1234";
    Base base = new Base (3);
    changeBase (base);
    System.out.println (base.i);
    changeStr (str);
    System.out.println (str);
  }
}

I thought I understood, but I still did n’t understand
changeBase modified the value of i according to the "object reference" rule,
But changeStr did not follow the "object reference" rule, still "1234"
why?

641695@qq.com

class Base
{
        public int i;
        public Base (int a)
        {
                i = a;
        }
}

public class StringTest {
  public static void changeStr (String str) {
    str = "welcome";
  }
  public static void changeBase (Base b)
  {
          b.i = 6;
  }
  
  public static void main (String [] args) {
    String str = "1234";
    Base base = new Base (3);
    changeBase (base);
    System.out.println (base.i);
    changeStr (str);
    System.out.println (str);
  }
}

37755500

String objects are a bit special
Once a String object is generated
You can never change it

seakey

The first change is to pass the object in, the "object reference" rule.
There is no transfer address in JAVA, so it is still "1234"

nanase

The first one is that object b object b cannot be changed
The second one is that string string cannot be changed directly

极度zs

You can change it like this
  public static String changeStr(String str){
    return "welcome";
  }
  public static void changeBase(Base b)
  {
  b.i=6;
  }
  
  public static void main(String[] args) {
    String str="1234";
    Base base = new Base(3);
    changeBase(base);
    System.out.println(base.i);
    str = changeStr(str);
    System.out.println(str);
  }

String is an immutable class and must display the result of the change

阿迪雅

Upstairs, I will try to quote what is the use of your return value

Upstairs upstairs:
The first one is that object b object b cannot be changed // but b has changed
The second one is that string string can't be directly changed naturally // this sentence is derived from the previous sentence, so this sentence is also not true

xhbsea

String and basic types are all fianl type! You can look at the book of reference passing and value passing

小小爬爬

str = changeStr(str); The effect of the statement is actually equivalent to

str = "welcome"; The return value is directly assigned to str, so the string displayed changes

dunke0921

I understand it this way: what changed is a copy of str