Java:如何解决组合框空值问题?
我正在研究一个简单的医院预约系统Java:如何解决组合框空值问题?,java,swing,windowbuilder,Java,Swing,Windowbuilder,我正在研究一个简单的医院预约系统 countyBox.addActionListener(新ActionListener(){ 已执行的公共无效操作(操作事件e){ 如果(!countyBox.getSelectedItem().toString().equalsIgnoreCase(null)和&!countyBox.getSelectedItem().toString().equalsIgnoreCase(“”){ if(cityBox.getSelectedItem().equals(“伊
countyBox.addActionListener(新ActionListener(){
已执行的公共无效操作(操作事件e){
如果(!countyBox.getSelectedItem().toString().equalsIgnoreCase(null)和&!countyBox.getSelectedItem().toString().equalsIgnoreCase(“”){
if(cityBox.getSelectedItem().equals(“伊斯坦布尔”)){
hospitalBox.removeAllItems();
迭代器遍历=hospitals.getIst(countyBox.getSelectedItem().toString()).Iterator();
while(traverse.hasNext()){
addItem(traverse.next());
}
}
else if(cityBox.getSelectedItem().equals(“Ankara”)){
hospitalBox.removeAllItems();
}
else if(cityBox.getSelectedItem().equals(“Izmir”)){
hospitalBox.removeAllItems();
}
}
}
});
在这段代码中,即使我从未触摸countyBox组合框,它仍然会进入条件。我给它一个条件,比如如果它为空,不要输入它,但它仍然输入。我做错了什么?这方面我是新手。注意:
某物。等于(null)
永远不会是真的
@真的吗?谢谢大家!@Seelenvirtuose为什么这样?如果something==null
调用comething.equals(…)
,会发生什么情况?@Seelenvirtuose对于正确的条件,我应该怎么做?
countyBox.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
if (!countyBox.getSelectedItem().toString().equalsIgnoreCase(null) && !countyBox.getSelectedItem().toString().equalsIgnoreCase("")) {
if (cityBox.getSelectedItem().equals("Istanbul")) {
hospitalBox.removeAllItems();
Iterator<String> traverse = hospitals.getIst(countyBox.getSelectedItem().toString()).iterator();
while (traverse.hasNext()) {
hospitalBox.addItem(traverse.next());
}
}
else if (cityBox.getSelectedItem().equals("Ankara")) {
hospitalBox.removeAllItems();
}
else if (cityBox.getSelectedItem().equals("Izmir")) {
hospitalBox.removeAllItems();
}
}
}
});