Day4 notes

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Common API

1.Random

It has a range of random number generation

ArrayList

ArrayList stores basic data types

String

String constant pool

Compare and precautions string

Because if str is null, "abc" .equals (str) returns false, and "str.equals (" abc ") will report null pointer exception

Common methods:

Ctrl + N level code can view the class

Static

Static memory map

Static code block

Arrays

Math