阅读ArrayList的JTextField的 [英] reading ArrayList JTextFields

问题描述

我的程序通过提示用户开始他们希望有多少文本字段有

 公共类textEvent1实现的ActionListener {//动作监听器有多少群众？
            公共无效的actionPerformed（ActionEvent的五）{
                N =（INT）（Double.parseDouble（massNumField.getText（）））;
 

接下来我创建了一个for循环来创建标签和文本框（这是我创建的列表，因为我不知道有多少会出现）。有一对夫妇名单，但我会给只是一个例子。

  ArrayList的群众=新的ArrayList（）;    的for（int i = 1; I＆LT; = N;我++）{//添加文本事件2文本屏幕
                        massLabel =新的JLabel（多少群众做弥撒+ I +有吗？）;
                        massField =新的JTextField，（5）;
                        masses.add（massField）;
 

现在我的问题似乎要来当我试图群众列表的元素赋值给一个变量，像这样。

 的for（int i = 1; I＆LT; = N;我++）{
                        质量= Double.parseDouble（（（的JTextComponent）masses.get（ⅰ））的getText（））;
 

我已经尝试了几件事情...质量= masses.get（我）......质量= masses.get（I）.getText（））等等等等。我要么不断收到错误，如空指针异常或事物说我不能parseDouble对象。

有错误的arrise这个例子是如下

 异常螺纹AWT-EventQueue的-0java.lang.ArrayIndexOutOfBoundsException：3＆GT; = 3
    在java.util.Vector.elementAt（来源不明）
    在acmx.export.java.util.ArrayList.get（ArrayList.java:54）
    在轨道$ textEvent2.actionPerformed（Orbit.java:151）
 

行151

 质量= Double.parseDouble（（（JTextComponent的）masses.get（I））的getText（））;
 

解决方案

创建当 JTextField的，你做的：

 的for（int i = 1; I＆LT; = N;我++）{
    ...
 

注意列表编号从0开始，所以当你获取一个类似的循环的项目，使用 I 作为索引，您试图访问一个过去的最后一个项目。更改阅读循环指数为：

 的for（int i = 0; I＆LT; N;我++）{
    ...
 

或者你可以使用增强的for循环，除非你需要用一个古老的Java版本：

 的（对象massField：群众）{
    质量= Double.parseDouble（（（的JTextComponent）massField）.getText（））;
    ...
 

（那么你真的应该使用泛型过，如果Java版本支持它们）。

My program starts by prompting the user how many text fields they would like to have

public class textEvent1 implements ActionListener {    //action listener for "how many masses?"
            public void actionPerformed (ActionEvent e) {
                n = (int)(Double.parseDouble(massNumField.getText())); 

next I create a for loop to create labels and textfields (which I have created lists for because I dont know how many there will be). There are a couple of lists but I will give an example of just one.

ArrayList masses = new ArrayList();

    for(int i=1; i<=n; i++) {                                  //adds text event 2 text to the screen
                        massLabel = new JLabel("How much mass does Mass " +i+ " have? ");
                        massField = new JTextField(5);
                        masses.add(massField);

Now my problem appears to come when I try to assign an element of the masses list to a variable like so.

for(int i=1; i<=n; i++) {
                        mass =  Double.parseDouble(((JTextComponent) masses.get(i)).getText());

I have tried a couple of things...mass = masses.get(i).....mass = masses.get(i).getText()) and so on and so on. I either keep getting errors such as Null pointer exceptions or things saying I cant parseDouble an Object.

There errors that arrise for this example are as below

Exception in thread "AWT-EventQueue-0" java.lang.ArrayIndexOutOfBoundsException: 3 >= 3
    at java.util.Vector.elementAt(Unknown Source)
    at acmx.export.java.util.ArrayList.get(ArrayList.java:54)
    at Orbit$textEvent2.actionPerformed(Orbit.java:151)

line 151 is

mass =  Double.parseDouble(((JTextComponent) masses.get(i)).getText());

解决方案

When creating the JTextFields, you do:

for(int i=1; i<=n; i++) {
    ...

Note that List indices start at 0, so when you retrieve the items with a similar loop, using i as the index, you are trying to access one past the last item. Change the reading loop indices to:

for (int i = 0; i < n; i++) {
    ...

Or you could use an enhance for loop, unless you need to use an ancient java version:

for (Object massField : masses) {
    mass =  Double.parseDouble(((JTextComponent) massField).getText());
    ...

(Then you should really use generics too, if the java version supports them).

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