Java基础

Java 基础

 

1. equals() and hasCode() 

(1). If two objects are equal, then they must have the same hash code.
(2). If two objects have the same hashcode, they may or may not be equal.

 

2.Exception Hierarchy in Java - Diagram

    Red colored are checked exceptions. Any checked exceptions that may be thrown in a method must either be caught or declared in the method’s throws clause. Checked exceptions must be caught at compile time.Checked exceptions are so called because both the Java compiler and the Java virtual machine check to make sure this rule is obeyed.