爪哇 - 强制实例化的

Question

类

我不断收到错误“InstantiationException”当我试图从我的自定义解串器运行，下面这段代码：

String attr = nel.getAttribute("class"); 
//happens when attr = "java.awt.Color" 
if (attr != null && !attr.isEmpty()){ 
    Object no = Class.forName(attr).newInstance(); <--- dies here 
    readObject(nel, no, true); 
    field.set(obj, no); 
} 

奇怪的是，它的工作在一个点，现在它不“T。

我该如何强制newInstance，然后设置该对象中的字段（readObject是否是我自己的函数）？

下面是一些调试信息：

java.lang.InstantiationException: java.awt.Color 
at java.lang.Class.newInstance0(Class.java:357) 
at java.lang.Class.newInstance(Class.java:325) 
at wms.lsw.tool.CustomXMLDecoder.readObject(CustomXMLDecoder.java:240) 
at wms.lsw.tool.CustomXMLDecoder.decode(CustomXMLDecoder.java:92) 
at wms.lsw.tool.Utils.openProject(Utils.java:716) 
at wms.lsw.tool.SecondaryMenuBar$2.actionPerformed(SecondaryMenuBar.java:52) 
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018) 
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341) 
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402) 
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259) 
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252) 
at java.awt.AWTEventMulticaster.mouseReleased(AWTEventMulticaster.java:289) 
at java.awt.Component.processMouseEvent(Component.java:6505) 
at javax.swing.JComponent.processMouseEvent(JComponent.java:3321) 
at java.awt.Component.processEvent(Component.java:6270) 
at java.awt.Container.processEvent(Container.java:2229) 
at java.awt.Component.dispatchEventImpl(Component.java:4861) 
at java.awt.Container.dispatchEventImpl(Container.java:2287) 
at java.awt.Component.dispatchEvent(Component.java:4687) 
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832) 
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492) 
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422) 
at java.awt.Container.dispatchEventImpl(Container.java:2273) 
at java.awt.Window.dispatchEventImpl(Window.java:2719) 
at java.awt.Component.dispatchEvent(Component.java:4687) 
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:723) 
at java.awt.EventQueue.access$200(EventQueue.java:103) 
at java.awt.EventQueue$3.run(EventQueue.java:682) 
at java.awt.EventQueue$3.run(EventQueue.java:680) 
at java.security.AccessController.doPrivileged(Native Method) 
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76) 
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87) 
at java.awt.EventQueue$4.run(EventQueue.java:696) 
at java.awt.EventQueue$4.run(EventQueue.java:694) 
at java.security.AccessController.doPrivileged(Native Method) 
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76) 
at java.awt.EventQueue.dispatchEvent(EventQueue.java:693) 
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:244) 
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:163) 
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:151) 
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:147) 
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:139) 
at java.awt.EventDispatchThread.run(EventDispatchThread.java:97) 

更新1

好，因为类颜色需要aruguments，我该怎么传递默认的东西一类，如果一类自动需要aruguments？或者有可能注入一个默认的构造函数？

谢谢。

Answer 1

应该是你试图调用静态方法的原因之一，你不需要调用newInstance()。

例如：

.... 
Class<?> c = Class.forName(attr); 
Class[] argTypes = new Class[] { String[].class }; 
Method main = c.getDeclaredMethod("main", argTypes); 
String[] mainArgs = Arrays.copyOfRange(args, 1, args.length); 

main.invoke(null, (Object)mainArgs); 
.... 

其他原因，你没有通过参数的构造函数（验证是否有默认值）

的参数使用：

MyClass c = MyClass .class.getConstructor(String.class).newInstance("some string"); 

Answer 2

newInstance()需要一个无参数的构造函数，并且Color没有这样的构造函数。

您需要找到合适的Constructor，然后使用它。