异常
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1.RuntimeException 以及其子类异常,在函数中被throw抛出,可以不try catch 不在函数上声明throws
2.继承需要注意:
①当一个方法被子类覆盖时,子类同名方法如果抛出异常,那么抛出的异常必须是父类的异常或者父类异常的子类。
②如果父类抛出多个异常,那么子类也要抛出多个异常,或者多个异常共有的子类异常。不能抛出新的父类没有的异常
③父类不抛出异常,那么子类也不能抛出异常
自定义异常
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class AgeException extends Exception { public String info; public AgeException(String info) { this.info = info; } public AgeException() { this("年龄异常!"); } public void printException() { System.out.println(info); } } class AgeTooBigException extends AgeException { public AgeTooBigException() { super("年龄太大!!!"); } } class AgeTooSmallException extends AgeException { public AgeTooSmallException() { super("年龄太小!!!"); } } class Person { private int age; public int getAge() { return age; } public void setAge(int age) throws AgeException { if (age > 200) { throw new AgeTooBigException(); } else if (age < 0) { throw new AgeTooSmallException(); } this.age = age; } }
Package
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1.对类文件进行分类管理
2.包必须是源文件的第一句话
3.其实类名的全称为: 包名.类名
4.包也是一种封装形式
包与包之间的访问以及修饰符的关系
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public protect default private
同类 √ √ √ √
同包 √ √ √
子类 √ √
不同包 √
cmd命令行打jar包
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1.cmd + jar cvf xxx.jar xxx.class xx.class xxxx.class
将 xxx.class ,xx.class, xxxx.class三个class文件,打入xxx.jar包中
注意 xxx.class ,xx.class, xxxx.class , xxx.jar 都是相对路径;必要时请使用绝对路径
2.cmd + jar cvf xxx.jar -C d:\xxx\xx/ *.class
将 d:\xxx\xx 文件夹下的所有 *.class文件打包到当前目录下,并且包名为xxx.jar
3.cmd + jar -tf xxx.jar
查看当前目录下xxx.jar包里面的文件
4.cmd + jar -cvfe xxxx.jar xx.xxx.xx.Dog -c ./ .
将当前目录下的所有文件打成xxxx.jar包,并且入口mian 函数为 xx.xxx.xx包下的Dog
5.cmd + java -jar xxxx.jar
运行当前目录下的xxxx.jar包,前提是xxxx.jar包有入口函数
6.cmd + java -cp d:\xx\xxx\x\xxx.jar xx.xxx.xx.Dog
运行d:\xx\xxx\x\xxx.jar包,并且以xx.xxx.xx.Dog为入口类
练习一:
三角形类自定义异常
定义三角形类(Triangle{a,c,b}),
要求:
a.两边和 > 第三边 ,抛出异常
b.a|b|c > 0 ,抛出异常
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public class Ts01 { public static void main(String[] args) throws Exception { Triangle t = new Triangle(1, 5, 6); Triangle t1 = new Triangle(-1, 5, 6); Triangle t2 = new Triangle(1, 5, 5); } } class Triangle { private int a; private int b; private int c; public Triangle(int a, int b, int c) throws Exception { if (a <= 0 || b <= 0 || c <= 0) throw new TooSmallException(); if (!checkLong(a, b, c)) throw new IllegalException(); this.a = a; this.b = b; this.c = c; System.out.println("三角形的边长为:" + a + "," + b + "," + c); } public boolean checkLong(int a, int b, int c) { if (a + b <= c || a + c <= b || b + c <= a) return false; else return true; } } class TooSmallException extends Exception { public String info; public TooSmallException() { this("发生异常:边长必须大于0!!!"); } public TooSmallException(String info) { this.info = info; } } class IllegalException extends Exception { public String info; public IllegalException() { this("发生异常:两边之和必须大于第三边!!!"); } public IllegalException(String info) { this.info = info; } }
全文完!