我如何知道一个类的实例是否已经存在于内存中？
我的问题是，如果类的实例存在，则不需要读取方法 这是我的代码
private void jButton (java.awt.event.ActionEvent evt) {
PNLSpcMaster pnlSpc = new PNLSpcMaster();
jtabbedPanel.addTab("reg",pnlSpc);
}
我想检查 PNLSpcMaster 的实例，当然我可以通过静态 boolean 值检查，但我认为这种方式更好。
最佳答案
如果你只想拥有一个“PNLSpcMaster”实例，那么你do need a singleton :
这是常见的单例习语:
public class PNLSpcMaster {
/**
* This class attribute will be the only "instance" of this class
* It is private so none can reach it directly.
* And is "static" so it does not need "instances"
*/
private static PNLSpcMaster instance;
/**
* Constructor make private, to enforce the non-instantiation of the
* class. So an invocation to: new PNLSpcMaster() outside of this class
* won't be allowed.
*/
private PNLSpcMaster(){} // avoid instantiation.
/**
* This class method returns the "only" instance available for this class
* If the instance is still null, it gets instantiated.
* Being a class method you can call it from anywhere and it will
* always return the same instance.
*/
public static PNLSpcMaster getInstance() {
if( instance == null ) {
instance = new PNLSpcMaster();
}
return instance;
}
....
}
用法:
private void jButton (java.awt.event.ActionEvent evt) {
// You'll get the "only" instance.
PNLSpcMaster pnlSpc = PNLSpcMaster.getInstace(); //<-- getInstance()
jtabbedPanel.addTab("reg",pnlSpc);
}
或者直接:
private void jButton (java.awt.event.ActionEvent evt) {
jtabbedPanel.addTab("reg",PNLSpcMaster.getInstace());
}
对于基本用法，Singleton Pattern效果很好。然而，对于更复杂的用法，它可能是危险的。
您可以阅读更多相关信息:Why singletons are controversial
关于java - 我怎么知道一个类的实例是否已经存在于内存中？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/1441984/