[英]Adding Integers to an Array in Java
I have to create a program that accepts user input of numbers and then adds them to an ArrayList and then manipulates the data in several ways. 我必须创建一个程序来接受用户输入的数字,然后将它们添加到ArrayList中,然后以几种方式处理数据。 The numbers must greater than or equal to 0. I am having an issue with adding the user input to the ArrayList, my try and catch statements stop the program from crashing but I can't add anything to the ArrayList, can someone tell me what I'm doing wrong in my adding process?
数字必须大于或等于0。我在将用户输入添加到ArrayList时遇到问题,我的try和catch语句阻止程序崩溃,但是我无法在ArrayList中添加任何内容,有人可以告诉我什么吗?添加过程中我做错了吗? Here's my code:
这是我的代码:
import java.util.ArrayList;
import java.util.Collections;
public class SumElements extends javax.swing.JFrame {
ArrayList <Integer> values = new ArrayList();
... ...
private void addButtonActionPerformed(java.awt.event.ActionEvent evt) {
try
{
//clear outputArea
outputArea.setText(null);
valueInput.setText(null);
outputLabel.setText(null);
//declare variables
int value = Integer.parseInt(valueInput.getText());
//validate input
if (value >= 0){
//add item to array
values.add(value);
//display values
Collections.sort(values);
for (int i = 0; i < values.size(); i++)
{
outputArea.setText(outputArea.getText() + values.get(i) + "\n");
}
}
}
//set default
catch (NumberFormatException a)
{
outputLabel.setText("Please input a valid number.");
}
}
This is because you set the text of valueInput
to null
(with valueInput.setText(null)
) before calling Integer.parseInt(valueInput.getText())
which will throw a NumberFormatException
of the following type: 这是因为你设置的文本
valueInput
到null
(用valueInput.setText(null)
之前调用) Integer.parseInt(valueInput.getText())
这将抛出一个NumberFormatException
的以下类型:
Exception in thread "main" java.lang.NumberFormatException: null
at java.lang.Integer.parseInt(Integer.java:542)
at java.lang.Integer.parseInt(Integer.java:615)
So simply remove the line valueInput.setText(null);
因此,只需删除行
valueInput.setText(null);
You can parse only those strings, which represents numbers. 您只能解析那些代表数字的字符串。 The String variable which is pointing to null is definitely not representing the number.
指向null的String变量绝对不代表数字。 What I would suggest is to modify the code in this way:
我建议以这种方式修改代码:
//declare variables
int value = Integer.parseInt(valueInput.getText());
//clear outputArea
valueInput.setText("");
outputLabel.setText("");
//validate input
if (value >= 0){
//add item to array
values.add(value);
//display values
Collections.sort(values);
for (int i = 0; i < values.size(); i++) {
outputArea.setText(outputArea.getText() + values.get(i) + "\n");
}
在完成对输入的解析并将其保存为变量之后,请// //清除outputArea!
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