抛出空指针异常

本文介绍了抛出空指针异常的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我在做Android的一个应用程序为我需要访问com.android.internal.telephony的API。现在我能够访问这些API，但问题是，无论我打电话类Call.java的 getEarliestConnection（）方法，我自己的类它抛出一个 NullPointerException异常。 你可以找到Call.java这里的http：// HI- android.info/src/com/android/internal/telephony/Call.java.html 。在这个类有以下方法：

I am doing one application in android for that I need to access com.android.internal.telephony APIs. Now I am able to access those APIs but problem is wherever I call the getEarliestConnection() method of Class Call.java in my own class it's throwing a NullPointerException. You can find Call.java here hi-android.info/src/com/android/internal/telephony/Call.java.html. In this class there is the following method:

1. public Connection 2. getEarliestConnection() { 3. List l; 4. long time = Long.MAX_VALUE; 5. Connection c; 6. Connection earliest = null; 7. 8. l = getConnections(); 9. 10. if (l.size() == 0) { 11. return null; 12. } for (int i = 0, s = l.size() ; i < s ; i++) { c = (Connection) l.get(i); long t; t = c.getCreateTime(); if (t < time) { earliest = c; time = t; } } return earliest; }

我想在我的课调用此方法。该类Call.java保险业监督一个抽象类，我创建的调用类的子类，这样调用上面的方法：

I want to call this method in my class. the class Call.java ia an abstract class I created subclass of Call class and called the above method like this:

Call myCall = new MyCall(); Connection myConn = new MyConn(); myConn = myCall.getEarliestConnection();

但它在网上抛出一个 NullPointerException异常 NO：10以上方法和行号：3以上code。

But It's throwing a NullPointerException on line no:10 of above method and line no:3 of above code.

推荐答案

显然 getConnections（）返回null这里，你无法得到空对象的大小。

Obviously getConnections() returns null here and you cannot get the size of the null-object.

下面是如何解决这个问题：

Here's how to fix it:

if (l == null || l.size() == 0) { return null; }

因此​​，如果由于某种未知的原因，也没有连接，列表或列表是空的，空将被退回。使用操作 || 会做一样的

So, if for some unknown reason, there is no Connection-List or the list is empty, null will be returned. Using the operator || will do the same as

if (l == null) { return null; } else if ( l.size() == 0) { return null; }