使用循环将元素添加到arraylist

Question

My problem is very simple but i can't find the way to solve it. Basically i want to create an Arraylist and add elements to it using a loop(up to as many elements as i want). i'm using the netbeans gui, and whenever i press a button "add" i want to add the string variables name and capital to my arraylist and display it in a TextArea. something like:

[london, england,america,united states etc..] 

so far the only thing it does is print the two variables name and capital many times like:

[londonn, england, london, england etc..]

here is the code:

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
    String name, capital;
    ArrayList<String> input = new ArrayList<>();
    name = jTextField1.getText();
    capital = jTextField2.getText();
    for(int i=0;i < 10;i++) {
        input.add(name);
        input.add(capital);
        jTextArea4.setText(String.valueOf(input));
    }      
}

Answer 1

尝试将jTextArea4.setText(String.valueOf(input))移到for loop之外

Answer 2

If you're wanting your ArrayList to continually grow, then you need to make it a class variable and not a local variable to you jButton1ActionPerformed .

Also take out the for loop. When you're adding a new name and capital, to your ArrayList , you only have to do it once.

Something like this:

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
    // Make sure input is a class variable and it will continue to grow                                         
    input.add(jTextField1.getText());
    input.add(jTextField2.getText());
    jTextArea4.setText(String.valueOf(input));      
}

Once your ArrayList is a class variable, you're going to want a way to either clear the ArrayList or remove items from it.

Answer 3

您需要将以下代码保留在循环之外：

jTextArea4.setText(String.valueOf(input));

Answer 4

you have to remove the for loop becuase you are storing the same values more than one time.

you can do like this.

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
String name, capital;
ArrayList<String> input = new ArrayList<>();
name = jTextField1.getText();
capital = jTextField2.getText();
    input.add(name);
    input.add(capital);
    jTextArea4.setText(String.valueOf(input));  

}

here are getting the name and capital values from the text fields and stroing in into the arraylist and then display the values of the arraylist in teh textfield4..

if you want to add as much elements you can do but when you are setting the jtextField4 you have to get the last element from the input arraylist becuause the arraylist object contains 10 stings.

like this

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
String name, capital;
ArrayList<String> input = new ArrayList<>();
name = jTextField1.getText();
capital = jTextField2.getText();
for(int i=0;i < 10;i++) {
    input.add(name);
    input.add(capital);
    jTextArea4.setText(String.valueOf(input.get(input.size)));
}      

}

I hope this will help you.

Answer 5

Completely remove the loop. And if you want that arraylist to be useful you must make it a class level variable

ArrayList<String> input = new ArrayList<>();

private void jButton1ActionPerformed(ActionEvent evt) {                                         
String name, capital;
name = jTextField1.getText();
capital = jTextField2.getText();
    input.add(name);
    input.add(capital);
    jTextArea4.setText(String.valueOf(input));

}