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Java

Java Generics Interface with List

Wildcards How to write a generic interface with List or Collection of implemented class of the interface? I encounter to this problem when I write a tree node interface, here is the details of the problem: I need to create an interface for the following two classes, how to write

Java Variables Hiding and Method Overriding

Method Overriding and Variable Hiding In Java, methods are overridden, but variables can only be hidden. In the case of method overriding, overriding methods completely replace the inherited methods but in variable hiding, the child class hides the inherited variables instead of replacing them which basically means that the object

Apache CollectionUtils subtract and removeAll difference

Maven Dependency org.apache.commons commons-collections4 4.1 Difference between subtract and removeAll You can use CollectionUtils.removeAll(collection, remove) or CollectionUtils.subtract(collection, remove) to remove certain element from collections, the difference is that the former can reuse element in remove variable, the later can not. The following is

How to Replace a Bean During Startup In Spring

There are circumstances in that we need to override a bean's methods which is from an external package but keep the same bean name. We can achieve this by replacing bean definition during application startup using BeanFactoryPostProcessor. BeanFactoryPostProcessor A BeanFactoryPostProcessor may interact with and modify bean definitions, but never bean

Spring Bean Lifecycle

Spring Bean Lifecycle

Lifecycle code example Executing above code, the printed messages would show in console in order as their number marks, which is exactly same as lifecycle image shows. above-mentioned LifeCycleDemoBeanPostProcessor:

First Initialization and Execution of ObjectMapper.readValue is Slow

I happened to find that first initialization and execution of ObjectMapper.readValue of an application is slow, no matter if I reuse static objectMapper or use new objectMapper instance every time, the first-time cost won't disappear. But overall, static objectMapper is faster than instance. The first execution would cost about