Attempt to invoke virtual method 'boolean java.lang.String.equals(java.lang.Object)' on a null object reference

这个错误通常是因为你在一个空对象上调用了equals方法。你需要确保该对象不为空，才能调用该方法。你可以使用if语句来检查该对象是否为空，例如：

if (myString != null) {
    if (myString.equals("someValue")) {
        // do something
    }
}

这样就能避免空引用错误了。

相关问题

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference

This error occurs when you are trying to invoke the 'toString()' method on a null object reference. The 'toString()' method is used to convert an object to a string representation. However, if the object is null, then there is no object to convert and this error is thrown.

To fix this error, you need to make sure that the object you are calling the 'toString()' method on is not null. You can do this by checking for null before calling the method, like this:

if (object != null) {
String stringRepresentation = object.toString();
// Do something with the string representation
}

Alternatively, you can use the null-safe operator '?' to avoid a NullPointerException like this:

String stringRepresentation = object?.toString();

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.String.trim()' on a null object reference

这个错误是因为你在一个空对象上调用了trim()方法。在Java中，如果一个对象是null，那么就无法调用其方法或访问其属性。因此，你需要先检查该对象是否为null，然后再调用其方法。例如：

if (str != null) {
    String trimmedStr = str.trim();
    // 在这里处理trimmedStr
} else {
    // 处理str是null的情况
}

这样就可以避免NullPointerException错误。