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POUsing multiple classes getting Null pointer exception. Probably syntactical.
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copied!<p>So I am supposed to make 3 classes and am given a 4th class to use for a user interface. One class (DBBinding) is supposed to have a String key and String value and take something like name:Alien or star: harry dean and make name or star be the "key" and the other is the "value" the next class (DBrecord) is to hold a group of these "bindings" as one record. I have chosen to keep a group of these bindings in a ArrayList. The third class(DBTable) is another ArrayList but of . I am at the point where I am reading in a line of txt from file where each line of txt is going to be one DBrecord that we know will be in correct formatting(key:value, key:value, key:value, and so on). </p> <p>Where I am having trouble is within the DBrecord class. I have a method(private void addBindingToRecord(String key_, String value_)) that is called from (public static DBrecord createDBrecord(String record)) from within the DBrecord class here are each methods code. I am having trouble with the addBindingToRecord method ... it null pointer exceptions on the first time used. I think it has to do with sytax and how I am calling the "this.myDBrecord.add(myDBBinding);"... have tried it multiple ways with same result....</p> <pre><code>public static DBrecord createDBrecord(String record)//takes a string and breaks it into DBBindings and makes a record with it. { DBrecord myRecord=new DBrecord(); String temp[]; temp=record.split(",",0); if(temp!=null) { for(int i=0; i<Array.getLength(temp); i++) { System.out.println("HERE");//for testing String temp2[]; temp2=temp[i].split(":",0); myRecord.addBindingToRecord(temp2[0], temp2[1]); } } return myRecord; } private void addBindingToRecord(String key_, String value_) { DBBinding myDBBinding=new DBBinding(key_, value_); if(myDBBinding!=null)//////////////ADDED this.myDBrecord.add(myDBBinding);///Here is where my null pointer exception is. } </code></pre> <p>I am going to post the full code of all my classes here so you have it if need to look at. Thank for any help, hints, ideas. </p> <pre><code>package DataBase; import java.io.*; public class CommandLineInterface { public static void main(String[] args) { DBTable db = new DBTable(); // DBTable to use for everything try { // Create reader for typed input on console BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); String line; while (true) { int length = 0; int selectedLength = 0; // YOUR CODE HERE System.out.println("\n" + length + " records (" + selectedLength + " selected)"); System.out.println("r read, p print, sa select and, so select or, da ds du delete, c clear sel"); System.out.print("db:"); line = reader.readLine().toLowerCase(); if (line.equals("r")) { System.out.println("read"); String fname; System.out.print("Filename:"); //fname = reader.readLine();////ADD BACK IN AFTER READ DEBUGED // YOUR CODE HERE fname="movie.txt"; db.readFromFile(fname); } else if (line.equals("p")) { System.out.println("print"); // YOUR CODE HERE DBTable.print(); } else if (line.equals("da")) { System.out.println("delete all"); // YOUR CODE HERE } else if (line.equals("ds")) { System.out.println("delete selected"); // YOUR CODE HERE } else if (line.equals("du")) { System.out.println("delete unselected"); // YOUR CODE HERE } else if (line.equals("c")) { System.out.println("clear selection"); /// YOUR CODE HERE } else if (line.equals("so") || line.equals("sa")) { if (line.equals("so")) System.out.println("select or"); else System.out.println("select and"); System.out.print("Criteria record:"); String text = reader.readLine(); // get text line from user // YOUR CODE HERE } else if (line.equals("q") || line.equals("quit")) { System.out.println("quit"); break; } else { System.out.println("sorry, don't know that command"); } } } catch (IOException e) { System.err.println(e); } } } package DataBase; import java.util.*; import java.io.*; public class DBTable { static ArrayList<DBrecord> myDBTable; public DBTable() { ArrayList<DBrecord> myDBTable= new ArrayList<DBrecord>(); } public static void addRecordToTable(DBrecord myRecord)//added static when added addRecordToTable in readFromFile { if(myRecord!=null) {myDBTable.add(myRecord);} } public static void readFromFile(String FileName) { try { FileReader myFileReader=new FileReader(FileName); String line="Start"; BufferedReader myBufferdReader=new BufferedReader(myFileReader); while(line!="\0") { line=myBufferdReader.readLine(); if(line!="\0") { System.out.println(line);//TEST CODE addRecordToTable(DBrecord.createDBrecord(line));// made addRecordToTable static. } } }catch(IOException e) {System.out.println("File Not Found");} } public static void print() { if (myDBTable==null) { System.out.println("EMPTY TABLE"); return; } else { for (int i=0; i<myDBTable.size(); i++) { System.out.println(myDBTable.get(i).toString()); } } } } package DataBase; import java.util.*; import java.lang.reflect.Array; //import DataBase.*;//did not help ... ? public class DBrecord { boolean select; String key; //need some type of collection to keep bindings. ArrayList<DBBinding> myDBrecord; public DBrecord() { //DBrecord myRecord=new DBrecord(); select=false; ArrayList<DBBinding> myDbrecord=new ArrayList<DBBinding>(); } private void addBindingToRecord(String key_, String value_) { DBBinding myDBBinding=new DBBinding(key_, value_); //System.out.println(myDBBinding.toString());//for testing if(myDBBinding!=null)//////////////ADDED this.myDBrecord.add(myDBBinding); System.out.println(key_);//for testing System.out.println(value_);//for testing } public String toString() { //out put key first then all values in collection/group/record. use correct formatting. StringBuilder myStringbuilder=new StringBuilder(); for (int i=0;i<this.myDBrecord.size();i++) { myStringbuilder.append(myDBrecord.get(i).toString()); myStringbuilder.append(", "); } myStringbuilder.delete(myStringbuilder.length()-2, myStringbuilder.length()-1);//delete last ", " thats extra return myStringbuilder.toString(); } public static DBrecord createDBrecord(String record)//takes a string and breaks it into DBBindings and makes a record with it. { //System.out.println("HERE");//for testing DBrecord myRecord=new DBrecord(); String temp[]; temp=record.split(",",0); if(temp!=null) { //System.out.println("HERE");//for testing //for(int i=0; i<Array.getLength(temp); i++) ///for testing //{System.out.println(temp[i]);} for(int i=0; i<Array.getLength(temp); i++) { System.out.println("HERE");//for testing String temp2[]; temp2=temp[i].split(":",0); System.out.println(temp2[0]);//for testing System.out.println(temp2[1]);//for testing myRecord.addBindingToRecord(temp2[0], temp2[1]); System.out.println(temp2[0]+ " "+ temp2[1]);////test code } } return myRecord; } } package DataBase; public class DBBinding { private String key; private String value; public DBBinding(String key_, String value_) { key =key_; value=value_; } public String getKey() {return key;} public String getValue() {return value;} public String toString() {return key+": "+value;} } </code></pre>

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