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"Pointers" in Java

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"Pointers" in Java

 
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  #1
May 16th, 2008
Hey,

I'm a C++ programmer, but I'm beginning to learn Java, and from what I see so far the two languages are very similar. The main difference I hear is that C++ has pointers and Java doesn't, but from my understanding Java does have pointers in a sense, the user is just not aware of it.

From what I've read in my book so far, I am under the impression that when you declare a variable of a complex data type (not sure if that's the right word, I mean like a self-defined class vs. an int) it is automatically a pointer. You cannot make it so that it is not a pointer. And when you declare a variable with a simple data type, it is not a pointer, and nothing you can do will make it a pointer? Is this assumption correct?

Like, this java code (sorry if there are minor syntax errors, as I'm used to C++):
java Syntax (Toggle Plain Text) 
  1. Student bill;
  2. bill = new Student();
  3. bill.GPA = 4.0;

is equivalent to this C++ code:
C++ Syntax (Toggle Plain Text) 
  1. Student* bill;
  2. bill = new Student;
  3. bill->GPA = 4.0;

Is that a correct "translation"?
I'm a student. If my statements seem too absolute, feel free to coat them with "In my opinion..." or "I believe...".
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duckman

Re: "Pointers" in Java

 
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  #2
May 17th, 2008
no. Java has no pointers as such.
Everything that's not a primitive is a reference.
While these act in some ways similarly to C++ pointers, they're more like C++ references.
As people are clearly allowed to attack me but I'm not allowed to defend myself, I no longer post to this site.
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Re: "Pointers" in Java

 
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  #3
May 18th, 2008
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Originally Posted by CoolGamer48 View Post
I am under the impression that when you declare a variable of a complex data type (not sure if that's the right word, I mean like a self-defined class vs. an int) it is automatically a pointer.
Yes, they are called "reference types". The references point to objects.
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Originally Posted by CoolGamer48 View Post
You cannot make it so that it is not a pointer.
You mean that you cannot have objects as values, then yes.

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Originally Posted by CoolGamer48 View Post
And when you declare a variable with a simple data type, it is not a pointer
Yes, they are called primitive types.

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Originally Posted by CoolGamer48 View Post
and nothing you can do will make it a pointer?
Basically. There is no way to "take the address" of a variable. But you can copy the value of the variable into a field of a wrapper object, which then can be pointed to by a reference.

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Originally Posted by CoolGamer48 View Post
Like, this java code (sorry if there are minor syntax errors, as I'm used to C++):
java Syntax (Toggle Plain Text) 
  1. Student bill;
  2. bill = new Student();
  3. bill.GPA = 4.0;

is equivalent to this C++ code:
C++ Syntax (Toggle Plain Text) 
  1. Student* bill;
  2. bill = new Student;
  3. bill->GPA = 4.0;

Is that a correct "translation"?
Yes.
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Re: "Pointers" in Java

 
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  #4
May 19th, 2008
First you must think whether a 'Refference' and a 'Pointer' are equivalent. Centainly not. And Java always use refference, not pointer (at least from programmer's point of view).

But I am not sure what happens inside JVM when it executes a class file. Since JVM is mainly written in C/C++, it is quite possible inside JVM somewhere (or in many places) pointer is used. Otherwise how can JVM adapter can access a file/directory or many things else?
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duckman

Re: "Pointers" in Java

 
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  #5
May 19th, 2008
1) it's reference, not refference
2) you don't need pointers to work with filesystems
3) JVMs don't have to be written in C++ or C
4) C/C++ doesn't exist
As people are clearly allowed to attack me but I'm not allowed to defend myself, I no longer post to this site.
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Re: "Pointers" in Java

 
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  #6
May 26th, 2008
Java Syntax (Toggle Plain Text) 
  1. 1) it's reference, not refference
  2.  

Thanks for the spelling correction

Java Syntax (Toggle Plain Text) 
  1. 2) you don't need pointers to work with filesystems
  2.  


Not in java but in C/C++. Pointers are often use in C/C++ to access files.

Java Syntax (Toggle Plain Text) 
  1. 3) JVMs don't have to be written in C++ or C
  2.  

Most Java Virtual Machines are written in C++, but at least one is written almost entirely in Java (Jalapeno from IBM). However other languages could also be used.

Java Syntax (Toggle Plain Text) 
  1. 4) C/C++ doesn't exist
  2.  

This sentence do not have any meaning!!!!! Clarify.
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Re: "Pointers" in Java

 
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  #7
May 26th, 2008
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Originally Posted by agdastidar View Post
Java Syntax (Toggle Plain Text) 
  1. 4) C/C++ doesn't exist
  2.  

This sentence do not have any meaning!!!!! Clarify.
The logic is that C is a programming language and C++ is a programming language, but C/C++ is a misunderstanding of the difference between C and C++. Edward thinks this is just the language snobs being snobbish, and there are enough legitimate meanings of C/C++ to let it go.
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Re: "Pointers" in Java

 
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  #8
May 27th, 2008
Edward thinks wrong...
If you can't even correctly define your problem domain how are you ever going to figure out a correct solution?
As people are clearly allowed to attack me but I'm not allowed to defend myself, I no longer post to this site.
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Re: "Pointers" in Java

 
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  #9
May 27th, 2008
I always thought C/C++ meant C or C++...
I'm a student. If my statements seem too absolute, feel free to coat them with "In my opinion..." or "I believe...".
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Re: "Pointers" in Java

 
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  #10
May 28th, 2008
nope, it's some kids' idea that C and C++ are actually one and the same language.
As people are clearly allowed to attack me but I'm not allowed to defend myself, I no longer post to this site.
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