我正在嘗試了解和之間的區別Hashtable，HashMap我正在嘗試在此處為這些商品添加特定價格。目標是將從中選擇的專案的價格列印comboItem到txtPrice.
String[] items = {"Select Item","Betta Fish","Snail","Supplies","Food"};
comboGroup = new JComboBox<String>(items);
comboGroup.addActionListener(this);
comboGroup.setBounds(130,35,150,40);
comboItem = new JComboBox<>();
comboItem.setPrototypeDisplayValue("XXXXXXXXXXX");
comboItem.setBounds(130,85,150,40);
String[] subItems1 = {"Select Betta","Plakat","Halfmoon","Double Tail","Crown Tail"};
subItems.put(items[1], subItems1);
String[] subItems2 = {"Select Snail","Pond Snail","Ramshorn","Apple Snail","Assassin Snail"};
subItems.put(items[2], subItems2);
String[] subItems3 = {"Select Supply","Small Fine Net","Large Fine Net","Flaring Mirror","Aquarium Hose (1meter)"};
subItems.put(items[3], subItems3);
String[] subItems4 = {"Select Food","Daphnia","Tubifex","Mosquito Larvae","Optimum Pellets"};
subItems.put(items[4], subItems4);
comboGroup.setSelectedIndex(1);
//TextFields <- this is the attempt to add price to subItems value but commented out
/*int[] items1price = {0,150,350,200,200};
subItems.put(items[1], items1price);
int[] items2price = {0,15,25,80,120};
subItems.put(items[2], items2price);
int[] items3price = {0,50,80,25,15};
subItems.put(items[3], items3price);
int[] items4price = {0,50,100,50,50};
subItems.put(items[4], items4price);
comboGroup.setSelectedIndex(1);
*/
txtPrice = new JTextField();
txtPrice.setBounds(130,135,150,40);
到目前為止，我對HashMap將其應用于 CLi 而不是在 GUI 中的理解，如果我嘗試，HashMap<String,Integer>我只能在一行中完全列印它。
例如。
HashMap<String,Integer> item = new HashMap<String,Integer>();
item.put("Plakat",50);
CLi Prints:
Plakat=50
我想要的是從選定的列印 PlakatcomboItem然后列印50到，txtPrice但我不知道該怎么做。
整個代碼在這里：https ://github.com/kontext66/GuwiPos GUI 和 Main。
附加說明：我是一個初學者，我現在正在嘗試理解布局管理器，所以這里的代碼有點混亂和文字。
uj5u.com熱心網友回復：
下面是一個示例，使用JComboBoxandHashMap獲取組合框中特定專案的相應“價格”。我建議閱讀有關如何使用各種布局管理器的教程，然后選擇最適合您的。至于和的區別HashMap，HashTable請看這個答案。主要區別在HashTable于是同步的，而HashMap不是，因為同步對你來說不是問題，我建議HashMap。此外，另一種選擇是將自定義物件的實體添加到 a JComboBox，如此處所述。因此，沒有必要使用HashMap.
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import java.util.*;
public class App {
Map<String, String> map;
JTextField tf;
public App() {
map = new HashMap<String, String>();
map.put("Plakat", "50");
map.put("Halfmoon", "25");
map.put("Double Tail", "80");
}
private void addComponentsToPane(Container pane) {
String[] items = { "Select Item", "Plakat", "Halfmoon", "Double Tail" };
JComboBox<String> comboBox = new JComboBox<String>(items);
comboBox.addItemListener(new ItemListener() {
public void itemStateChanged(ItemEvent event) {
if (event.getStateChange() == ItemEvent.SELECTED) {
String item = (String) event.getItem();
System.out.println(item);
tf.setText(map.get(item));
}
}
});
tf = new JTextField();
JPanel p = new JPanel();
pane.add(comboBox, BorderLayout.NORTH);
pane.add(tf, BorderLayout.SOUTH);
}
private void createAndShowGUI() {
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
addComponentsToPane(frame.getContentPane());
// frame.setSize(640, 480);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
new App().createAndShowGUI();
}
});
}
}
更新
下面是前面描述的第二種方法的實作，其中使用自定義物件將專案添加到 a JComboBox，因此不需要使用 a HashMap。
PS我還應該補充一點，如果不允許用戶在文本欄位中編輯“價格”，那么你應該使用tf.setEditable(false);，甚至使用 aJLabel代替。
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
public class App {
JTextField tf;
class ComboItem {
private String key;
private String value;
public ComboItem(String key, String value) {
this.key = key;
this.value = value;
}
@Override
public String toString() {
return key;
}
public String getKey() {
return key;
}
public String getValue() {
return value;
}
}
private void addComponentsToPane(Container pane) {
JComboBox<ComboItem> comboBox = new JComboBox<ComboItem>();
comboBox.addItem(new ComboItem("Select Item", ""));
comboBox.addItem(new ComboItem("Plakat", "50"));
comboBox.addItem(new ComboItem("Halfmoon", "25"));
comboBox.addItem(new ComboItem("Double Tail", "80"));
comboBox.addItemListener(new ItemListener() {
public void itemStateChanged(ItemEvent event) {
if (event.getStateChange() == ItemEvent.SELECTED) {
Object item = comboBox.getSelectedItem();
String value = ((ComboItem) item).getValue();
tf.setText(value);
}
}
});
tf = new JTextField();
JPanel p = new JPanel();
pane.add(comboBox, BorderLayout.NORTH);
pane.add(tf, BorderLayout.SOUTH);
}
private void createAndShowGUI() {
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
addComponentsToPane(frame.getContentPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
new App().createAndShowGUI();
}
});
}
}
更新 2
要將文本欄位中的字串轉換為雙精度，您可以使用Double.parseDouble(String)，如下所示（再次確保使用tf.setEditable(false);，以便用戶無法修改該值）。
double price = 0;
if (tf.getText() != null && !tf.getText().trim().isEmpty())
price = Double.parseDouble(tf.getText());
System.out.println(price);
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