android - How to delete all Table records in Sqlite? -

i json value server , save data database in sqlite in android, create database , table sqliteopenhelper class:

public class activitytabledbopenhelper extends sqliteopenhelper {  private static final string logtag = "atdbopenhelper";  private static final string database_name = "mydatabase.db"; private static final int database_version = 1;  public static final string activity_table = "'activity'"; public static final string column_activity_id = "'activityid'"; public static final string column_user_id = "'userid'"; public static final string column_program_id = "'programid'"; public static final string column_order = "'order'"; public static final string column_g_date = "'gdate'"; public static final string column_j_date = "'jdate'";  private static final string table_create =         "create table " + activity_table + " (" +                 column_activity_id + " integer(20), " +                 column_user_id + " integer(20), " +                 column_program_id + " integer(20), " +                 column_order + " varchar(200), " +                 column_g_date + " varchar(200), " +                 column_j_date + " varchar(200) " +                 ")";  public activitytabledbopenhelper(context context) {     super(context, database_name, null, database_version); }  @override public void oncreate(sqlitedatabase db) {     db.execsql(table_create);     log.i(logtag, "activity table has been created!"); }  @override public void onupgrade(sqlitedatabase db, int oldversion, int newversion) {     db.execsql("drop table if exists" + activity_table);     oncreate(db); } 

}

i can insert data activity table, want delete records when user click button, use line code , error:

sqlitedatabase database; database.delete(activitytabledbopenhelper.activity_table,null,null);  

this activity class:

@override     protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.activity_activity_table);           btndeleteatdata = (button) findviewbyid(r.id.btndeleteatdata);           datasource = new activitytabledatasource(this);         datasource.open();           btndeleteatdata.setonclicklistener(new view.onclicklistener() {             @override             public void onclick(view v) {                 database=new sqlitedatabase();                   database.delete(activitytabledbopenhelper.activity_table,null,null);             }         });            } 

this error:

java.lang.nullpointerexception: attempt invoke virtual method 'int android.database.sqlite.sqlitedatabase.delete(java.lang.string, java.lang.string, java.lang.string[])' on null object reference             @ com.rastari.salar.salytest.activitytableactivity$2.onclick(activitytableactivity.java:69)             @ android.view.view.performclick(view.java:4780)             @ android.view.view$performclick.run(view.java:19866)             @ android.os.handler.handlecallback(handler.java:739)             @ android.os.handler.dispatchmessage(handler.java:95)             @ android.os.looper.loop(looper.java:135)             @ android.app.activitythread.main(activitythread.java:5254)             @ java.lang.reflect.method.invoke(native method)             @ java.lang.reflect.method.invoke(method.java:372)             @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:903)             @ com.android.internal.os.zygoteinit.main(zygoteinit.java:698) 

how can delete records activity table?

thank you.

you should first initialize sqlitedatabase, convert this:

sqlitedatabase database; database.delete(activitytabledbopenhelper.activity_table,null,null);  

to this:

sqlitedatabase database = new sqlitedatabase(this); // or dbhelper.getwritabledatabase(); if have dbhelper database.delete(activitytabledbopenhelper.activity_table,null,null); 

else database object null , error. here find whole example operations http://www.vogella.com/tutorials/androidsqlite/article.html