char[] cbuf = new char[]

[Vikki Fiawoo]

Good Evening,

Below is a sample code using StringBuffer and char [] cbuf.

I am trying to understand the purpose of using the char [] cbuf in the code. I have included comments as to how I have decipher the code.
If you can please provide feedback, by removing or editing any part of the comments that I have included that is not true or does not apply, so that I can better understand this piece of code. I have worked with BufferedReader before but not really StringBuffer, so I am lost here.

   public static String readFile(String filePath)throws java.io.IOException{
        
        //This is the maximum capacity of characters allowed in the file that is being read??
        StringBuffer dataFromFile = new StringBuffer(1000);
		
       //Object used to read the data in the file
        BufferedReader reader = new BufferedReader (new FileReader(filePath));
        
        //Maximum number of characters allowed??
        char[] cbuf = new char[1024];
        
        //variable to hold the total number of characters found in the file
        int numRead=0;
        
        //verifies if the number characters in the file does not equal negative 1??
        while((numRead=reader.read(cbuf)) != -1){
            
           //Returns the string representation of a cbuf??
        	String readData = String.valueOf(cbuf, 0, numRead);
            //appends the string
        	dataFromFile.append(readData);
            //set cbuf back to 1024 characters allowed??
        	cbuf = new char[1024];
        }
        
        reader.close();
        
        //convert the data in the StringBuffer to String object
        return dataFromFile.toString();
    }

[Henry Wong]

        //This is the maximum capacity of characters allowed in the file that is being read??
        StringBuffer dataFromFile = new StringBuffer(1000);

The parameter is for initial capacity. The stringbuffer can grow bigger than that.

        //Maximum number of characters allowed??  
        char[] cbuf = new char[1024];  

This is the character buffer that will be used to store the read bytes. And since it is sized at 1K, that will be the maximum that can be returned in a single read() call.

Henry

[Matthew Brown]

Vikki Fiawoo wrote:

        //verifies if the number characters in the file does not equal negative 1??
        while((numRead=reader.read(cbuf)) != -1){

If you look at the Javadocs for java.io.Reader#read(char[]), it describes the return value as "The number of characters read, or -1 if the end of the stream has been reached". So this line keeps looping, reading characters into the cbuf array, until the end of the file.

The Javadocs should generally be your first port of call for understanding what methods do for classes in the core libraries.

[Vikki Fiawoo]

Hi Henry,

Thank you for your explanation. It really helped me.

Could you please elaborate a little further on the this part of the code?

//Returns the string representation of a cbuf??   
String readData = String.valueOf(cbuf, 0, numRead); 

[Mike Simmons]

Check out the API for java.lang.String (<-- that's a link) and look at the valueOf() method. Specifically, look at the one that takes three arguments, of the types given in the example.

[Paul Adcock]

reader.read(cbuf))

There is a read I think that takes no params and another that takes 3. I don't see a read(char[]) in the BufferedReader API. (At least not in Java 7 SE.)

[Mike Simmons]

It's there. You have to look also at the methods inherited from superclasses, such as java.io.Reader in this case.

[D. Ogranos]

Vikki Fiawoo wrote:Could you please elaborate a little further on the this part of the code?

//Returns the string representation of a cbuf??   
String readData = String.valueOf(cbuf, 0, numRead); 

This is a BAD thing to do. You create a new String with the read chars here, and thats totally unneccessary. As others said above, go and check the API for the classes you use. In this case, StringBuffer: You will see that there is an append() method which allows you to directly append data from a char[] to the buffer.

[Rob Spoor]

D. Ogranos wrote:In this case, StringBuffer

I'd recommend StringBuilder over StringBuffer, as you don't need the synchronization StringBuffer provides.