C/C #/java strange parameter passing and interpretation

Let's take a look at the C language code below.

#include <stdio.h>void s(char *b){    printf("%s\n",b);    b="aaaa";    printf("%s\n",b);}int main(){    char *a="hello";    s(a);    printf("%s\n",a);}

The output of my first impression should be changed

Hello

Aaaa

Aaaa

But this is wrong.

The actual output is

 

Hello

Aaaa

Hello

Isn't it weird? Actually Think About It. C language parameters are actually passed values (pointers are also passed pointer values). When s (a) is called, the stack opens up a parameter zone to pass the pointer value of. When the statement B = "aaaa"; is executed, the B pointer value in the parameter area is changed to the address of "aaaa", but the value of a is not changed, therefore, when the main function runs printf ("% s \ n", a);, the original value is printed. Let's look at the java code.

public void extractXPS(StringWriter sw) {    sw=new StringWriter();    sw.write("Hello World");}void m(){    StringWriter sw=new StringWriter();　　System.out.println(sw.toString());　　　　　　　　}

What kind of output will be produced by the execution method m?

Only "" is output, that is, "Hello World" is not output ".

In java and C #, the object parameter actually passes a reference (= pointer), which can be modified. However, if you point to another object again, after jumping out of this method, it does not affect the original objects in the original caller.