1、final定义:
·final用于声明属性,方法,形参和类
**(1)属性:定义就必须直接赋值或者在构造方法中进行赋值,并且后期都不能修改。**
public class Demo {
//final修饰属性必须要赋初值
public final int a = 1;
public final int b ;
public Demo() {
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