不能用JavaBeans制作程序来监听其他组件
这里有Purchase和PurchaseView类:不能用JavaBeans制作程序来监听其他组件,java,javabeans,Java,Javabeans,这里有Purchase和PurchaseView类: import java.beans.PropertyVetoException; public class Main { public static void main(String[] args) { Purchase purch = new Purchase("Computer"); PurchaseView pView = new PurchaseView(); purch.addPropertyCha
import java.beans.PropertyVetoException;
public class Main {
public static void main(String[] args) {
Purchase purch = new Purchase("Computer");
PurchaseView pView = new PurchaseView();
purch.addPropertyChangeListener(pView);
try {
purch.setData("Notebook");
System.out.println(purch);
} catch (PropertyVetoException exc) {
System.out.println(exc.getMessage());
}
}
}
我希望程序在数据属性更改时生成PurchaseView类中显示的输出。对我来说,它似乎得到了很好的实施,但不起作用
有什么想法吗?你的想法是什么
我想你刚才在setData方法中使用旧值时犯了一个错误。应该是这样的:
import java.beans.PropertyChangeListener;
import java.beans.PropertyChangeSupport;
import java.beans.PropertyVetoException;
public class Purchase {
private String data;
private PropertyChangeSupport propertyChange = new PropertyChangeSupport(this);
public Purchase(String data) {
this.data = data;
}
public synchronized void addPropertyChangeListener(PropertyChangeListener listener) {
propertyChange.addPropertyChangeListener(listener);
}
public synchronized void removePropertyChangeListener(PropertyChangeListener l) {
propertyChange.removePropertyChangeListener(l);
}
public String getData() {
return data;
}
public void setData(String data) {
String oldValue = data;
this.data = data;
propertyChange.firePropertyChange("data", oldValue, data);
}
}
}
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
public class PurchaseView implements PropertyChangeListener{
public PurchaseView() {}
@Override
public void propertyChange(PropertyChangeEvent evt) {
String propName = evt.getPropertyName();
if(propName.equals("data")) {
String oldValue = (String) evt.getOldValue();
String newValue = (String) evt.getNewValue();
System.out.println("Change value of: " + evt.getPropertyName() + " from: " + oldValue + " to: " + newValue);
}
}
}
注意你忘记了setData方法第一行的
这个
保留字,这意味着你取的是方法变量而不是类变量。我的输出中没有任何内容。我实际上解决了这个问题。它与变量命名有关。我区分了数据和这个数据,但我的程序没有。我有一些类似于你的解决方案,但它不起作用。我将方法参数的名称从'data'更改为'aData',firePropertyChange传递了'aData'变量,它工作正常。
public void setData(String data) {
String oldValue = this.data;
this.data = data;
propertyChange.firePropertyChange("data", oldValue, data);
}