Exception in thread main java lang nullpointerexception arraylist

I' d write it this way. Works fine when I test it: public static List< File> getAllChildFiles( File[ ] dir) { List< File> result = new ArrayList< File> ( ) ; for ( File file : dir) { if ( file. isDirectory( ) ) { File[ ] children = file. listFiles( ) ; List< File>. You are never initializing the variables rand or bag, so they are always null. In your constructors you need to use rand and bag, not Rand or Bag. For example: public RandomBag( ) { bag = new ArrayList< E> ( ) ; rand = new. You forgot to create the objects for ( int x= 0; x< staging1. length; x+ + ) { staging1[ x] = new WinCalc( ) ; / /. FileNotFoundException: votes.

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    Arraylist exception nullpointerexception

    txt ( The system cannot find the file specified). You catch this error and set the matrix to null. int[ ] [ ] matrix1= load( " votes. txt" ) ; if( matrix1! = null) { / / in this case an exception has occured during read. List< List< Integer> > data = new ArrayList< List< Integer> > ( ) ;. For your second question, you should really start another thread. It is correctly printing the string representation of your object. Your Book class does not provide a custom overridden toString( ) method. So it uses the one. 参考にしていただければと思う。 目次 [ hide]. 1 Javaのエラー表示について; 2 Javaの エラーとその対策. NullPointerException; 2.

    int list[ ] = new int[ 10] ;. Exception in thread " main" java. Based on the code you' ve published, your array ArrayList < User> child is null. This will cause a NullPointerException the first time you try to access it on this line for ( User U : child) {. You need to initialize the child array. NullPointerException at com. tutorial; / / Package statement / / Imports class ArrayList from. You never instantiate storedStrings. Try changing: private ArrayList< String> storedStrings;. To: private ArrayList< String> storedStrings = new ArrayList< String > ( ) ;. When you have the line: this.