Java review

I'm going to use Java for the first time in a while, so I've summarized what I reviewed as a memorandum. It would be helpful if you could point out any mistakes ...

Java overview

--Developed by Sun Microsystems in the early 1990s --Sun Microsystems was acquired by Oracle in 2010 --The catch phrase is "Write Once, Run Anywhere"


--Java code consists of classes, and classes consist of states (instance variables) and functions (methods).



ArrayList<Integer> list = new ArrayList<Integer>();
list.add(1); //Insert int type data
int i = list.get(o); //Receive as an int type variable

Access level

Garbage collection



try {} catch(Exception e) {}

--Not recommended, but effective because it is convenient for test code etc.

try {
} catch(Cat e) {
} catch(Animal e) {



data structure

public void barkAll(ArrayList<Animal> user) {}

--When assigning a collection whose elements are subclass instances (using wildcards)

public void barkAll(ArrayList<? extends Animal> user) {}

Package and JAR

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