Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As _
  System.EventArgs) Handles Button1.Click
        Dim oradb As String = "Data Source=XE;User" & _
        "Id=cmattausch;Password=Sch@0401;"
        Dim conn As New OracleConnection(oradb)
        Dim adap As New OracleDataAdapter("select TABLE_NAME from ALL_TABLES", _
          conn)
        Dim dt As New DataTable
        adap.Fill(dt)
        Dim row As DataRow
        For Each row In dt.Rows
            IstTables.Items.Add(row("Table_Name"))
        Next
    End Sub

Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As _
  System.EventArgs) Handles Button2.Click
        Dim oradb As String = "Data Source=XE;User" & _
        "Id=cmattausch;Password=Sch@0401;"
        Dim conn As New OracleConnection(oradb)
        Dim adap As New OracleDataAdapter("select COLUMN_NAME from MA", conn)
        Dim dt As New DataTable
        adap.Fill(dt)
        Dim row As DataRow
        For Each row In dt.Rows
            IstTables.Items.Add(row("Column_Name"))
        Next
    End Sub