我将3个组合框添加到根据第一个组合框的选择更改2个组合框的形式。这里，当选择一个类别时，子类别将加载到一个组合框，尺寸将加载到下一个组合框。第一个组合框选择中的编码如下所示
private void jCcatItemStateChanged(java.awt.event.ItemEvent evt) {
//jlsubtype.removeAll();
System.out.println(jCcat.getSelectedItem().toString());
if (jCcat.getSelectedItem().toString().matches("Uniform")) {
jCsubCat.removeAllItems();
jCsubCat.addItem("Long Sleeve");
jCsubCat.addItem("Short Sleeve");
jCsubCat.addItem("Overcoat");
jCsubCat.addItem("Overoll");
} else if (jCcat.getSelectedItem().toString().matches("Headwear")) {
jCsubCat.removeAllItems();
jCsubCat.addItem("Caps");
jCsubCat.addItem("Scaffs");
} else if (jCcat.getSelectedItem().toString().matches("Footwear")) {
jCsubCat.removeAllItems();
jCsubCat.addItem("Shoes");
jCsubCat.addItem("Slippers");
}
if (jCcat.getSelectedItem().toString().matches("Uniform")) {
jCsSize.removeAllItems();
jCsSize.addItem("XS");
jCsSize.addItem("S");
jCsSize.addItem("M");
jCsSize.addItem("L");
jCsSize.addItem("XL");
jCsSize.addItem("XXL");
jCsSize.addItem("XXXL");
} else if (jCcat.getSelectedItem().toString().matches("Headwear")) {
jCsSize.removeAllItems();
jCsSize.addItem("Free Size");
} else if (jCcat.getSelectedItem().toString().matches("Footwear")) {
jCsSize.removeAllItems();
jCsSize.addItem("35");
jCsSize.addItem("36");
jCsSize.addItem("37");
jCsSize.addItem("38");
jCsSize.addItem("39");
jCsSize.addItem("40");
jCsSize.addItem("4");
jCsSize.addItem("5");
jCsSize.addItem("6");
jCsSize.addItem("7");
jCsSize.addItem("8");
jCsSize.addItem("9");
}
}
*然后更改第二个组合框的类型，将其加载到列表框中。该代码如下所示
private void jCsubCatItemStateChanged(java.awt.event.ItemEvent evt) {
if (jCcat.getSelectedItem().toString().matches("Uniform")) {
DefaultListModel lists = new DefaultListModel();
try {
Class.forName("com.mysql.jdbc.Driver").newInstance();
//Connection con = DriverManager.getConnection("jdbc:sqlserver://10.228.59.2:1433;databaseName=uniforminventorydb;user=SA;password=KreedaIntimo@2017;");
Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/uniforminventorydb", "root", "");
Statement st = con.createStatement();
PreparedStatement pst;
String Catagory;
String Type;
Catagory = jCcat.getSelectedItem().toString();
Type = jCsubCat.getSelectedItem().toString();
String sql = "Select Distinct SubType from add_stock Where Catergory = '" + Catagory + "' and Type = '" + Type + "'";
pst = con.prepareStatement(sql);
ResultSet rs = pst.executeQuery();
while (rs.next()) {
System.out.println(rs.getString(1));
String ls = rs.getString(1);
lists.addElement(ls);
jLsType.setModel(lists);
}
} catch (Exception e) {
e.printStackTrace();
}
} else if (jCcat.getSelectedItem().toString().matches("Footwear")) {
DefaultListModel lists = new DefaultListModel();
try {
Class.forName("com.mysql.jdbc.Driver").newInstance();
//Connection con = DriverManager.getConnection("jdbc:sqlserver://10.228.59.2:1433;databaseName=uniforminventorydb;user=SA;password=KreedaIntimo@2017;");
Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/uniforminventorydb", "root", "");
Statement st = con.createStatement();
PreparedStatement pst;
String Catagory;
String Type;
//Catagory = jCcat.getSelectedItem().toString();
Catagory = "Footwear";
Type = jCsubCat.getSelectedItem().toString();
String sql = "Select Distinct SubType from add_stock Where Catergory = '" + Catagory + "' and Type = '" + Type + "'";
pst = con.prepareStatement(sql);
ResultSet rs = pst.executeQuery();
while (rs.next()) {
System.out.println(rs.getString(1));
String ls = rs.getString(1);
lists.addElement(ls);
jLsType.setModel(lists);
}
} catch (Exception e) {
e.printStackTrace();
}
} else if (jCcat.getSelectedItem().toString().matches("Headwear")) {
DefaultListModel lists = new DefaultListModel();
try {
Class.forName("com.mysql.jdbc.Driver").newInstance();
//Connection con = DriverManager.getConnection("jdbc:sqlserver://10.228.59.2:1433;databaseName=uniforminventorydb;user=SA;password=KreedaIntimo@2017;");
Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/uniforminventorydb", "root", "");
Statement st = con.createStatement();
PreparedStatement pst;
String Catagory;
String Type;
// Catagory = jCcat.getSelectedItem().toString();
Catagory = "Headwear";
//Type = jCsubCat.getSelectedItem().toString();
String sql = "Select Distinct SubType from add_stock Where Catergory = '" + Catagory + "'";
pst = con.prepareStatement(sql);
ResultSet rs = pst.executeQuery();
while (rs.next()) {
System.out.println(rs.getString(1));
String ls = rs.getString(1);
lists.addElement(ls);
jLsType.setModel(lists);
}
} catch (Exception e) {
e.printStackTrace();
}
}
将类别更改为鞋类后运行此代码时，会出现以下错误
java.lang.NullPointerException
at uniforminventorysystem.HomeAdmin.jCsubCatItemStateChanged(HomeAdmin.java:2068)
at uniforminventorysystem.HomeAdmin.access$600(HomeAdmin.java:47)
ps.i已为第一个组合框加载了项，其方法如下：
//选择分类方法
private void catergorySelect(){
try {
Class.forName("com.mysql.jdbc.Driver").newInstance();
//Connection con = DriverManager.getConnection("jdbc:sqlserver://10.228.59.2:1433;databaseName=uniforminventorydb;user=SA;password=KreedaIntimo@2017;");
Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/uniforminventorydb", "root", "");
String sql = "select * from catergoryLoad";
pst = con.prepareStatement(sql);
ResultSet r = pst.executeQuery();
while (r.next()) {
jCcat.addItem(r.getString("Catergory"));
jCrcat3.addItem(r.getString("Catergory"));
jCocat.addItem(r.getString("Catergory"));
}
con.close();
} catch (Exception e) {
JOptionPane.showMessageDialog(null, "Failed to Connect to Database", "Error Connection", JOptionPane.WARNING_MESSAGE);
System.exit(0);
}
}
请给我解决这个问题的方法