Array[0] causes NullPointerException

Core Library Questions

mrumunhum

Array[0] causes NullPointerException

in Core Library Questions • 2 years ago

Hi group,

I have a script that has many problems: The first one is:

Exception in thread "Animation Thread" java.lang.NullPointerException
   at I2C_Plot.setup(I2C_Plot.java:33)
   at processing.core.PApplet.handleDraw(Unknown Source)
   at processing.core.PApplet.run(Unknown Source)
   at java.lang.Thread.run(Thread.java:636)

This is caused by this line "Old[0] = 0;".

The next problem is the clientEvent is being called all the time. It is only to be called when there is data from the Server.

Here is the script:

import processing.net.*;

Client C;
String data;
int X = 1;
int[] Old;
int[] Now;

void setup() {
size(600,200); smooth(); background( 0 );
C = new Client( this, "127.0.0.1", 5204 );
Old[0] = 0;
}

void draw() { }

void clientEvent( Client C ) {
println("Event"); int Yes;
while( ( Yes = C.available() ) > 0 ) {
    println("read: " + Yes);
    data = C.readStringUntil( '\n' );
    print(data);
    Now = int( splitTokens( data, " \n" ) );
    println(data);
    if( Now[0] != Old[0] ) { line( X, 10, X, 20 ); }
    point( X, 10 + ( Now[0] * 10 ) );
    Old[0] = Now[0];
    if( ++X > 600 ) X = 1;
}
}

Any ideas? Thanks for your time.

William Estrada
Mt Umunhum, CA, USA
HTTP://64.124.13.3 ( Mt-Umunhum-Wireless.net )
Skype: MrUmunhum

Replies(2)

jeff_g

Re: Array[0] causes NullPointerException

2 years ago

You define Old as an array, but you never create it. You must define the size of an array.

int[] Old;
void setup() {
Old = new int[10]; //This creates an int array that has a length of 10 (0-9)
}

int[] Old = new int[5]; //creates a int array that has a length of 5 (0-4)

In your case, you'd want to do something like this I guess..

int[] Old = new int[1];

but if it only has a length of 1, you don't need an array.
so you could just do this..

int Old;
Old = 0;

Anyhow... here is some working code.

import processing.net.*;
Client C;
String data;
int X = 1;
int[] Old = new int[1];
int[] Now = new int[1];
void setup() {
size(600,200); smooth(); background( 0 );
C = new Client( this, "127.0.0.1", 5204 );
Old[0] = 0;
}
void draw() { }
void clientEvent( Client C ) {
println("Event"); int Yes;
while( ( Yes = C.available() ) > 0 ) {
println("read: " + Yes);
data = C.readStringUntil( '\n' );
print(data);
Now = int( splitTokens( data, " \n" ) );
println(data);
if( Now[0] != Old[0] ) { line( X, 10, X, 20 ); }
point( X, 10 + ( Now[0] * 10 ) );
Old[0] = Now[0];
if( ++X > 600 ) X = 1;
}
}

mrumunhum

[Solved] Re: Array[0] causes NullPointerException

2 years ago

Thanks Jeff, I went to the flats yesterday and bought the book. Found the answer
on the last page by accident.

I am open another ticket about the clientEvent problem which I think is also my code.

Thanks for your time.

William Estrada
Mt Umunhum, CA, USA
HTTP://64.124.13.3 ( Mt-Umunhum-Wireless.net )
Skype: MrUmunhum

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