異常鏈?zhǔn)纠a注釋

一直覺得異常是一個(gè)過不去的坎，因?yàn)橥﹄y理解的。

對(duì)著慕課網(wǎng)老師的示例，手動(dòng)敲了代碼，并一步步加上syso跟蹤，終于對(duì)異常throw/throws有更深的理解，現(xiàn)在把驗(yàn)證代碼和注釋貼上來，希望和有疑惑的同學(xué)一起交流。

package?com.imooc.season3;

public?class?ThrowDemo?extends?Exception?{

			//TODO:?自定義Java?Exception	，繼承Exception父類
	
	public?ThrowDemo(){?//construtor函數(shù)構(gòu)造器,無參
		
	}
	
	public?ThrowDemo(String?s){
		super(s);
		System.out.println("Here?is?ThrowDemo(String?s)");
	}
}

package?com.imooc.season3;

public?class?ThrowDemoTest?{

	public?void?test01()?throws?ThrowDemo{?//throws?declaration聲明該方法有異常拋出
		System.out.println("step02:Reach?test01，new?ThrowDemo?初始化函數(shù)構(gòu)造器--》ThrowDemo異常對(duì)象，并拋出throw?e");
		throw?new?ThrowDemo("test01拋出異常");??//throw?拋出異常的動(dòng)作
	}
	
	public?void?test02(){
		try?{
			System.out.println("step01:準(zhǔn)備運(yùn)行test01");
			test01();
		}?catch?(ThrowDemo?e)?{???//方法test01中會(huì)拋出異常，因此調(diào)用該方法的時(shí)候就try?catch它預(yù)料中的異常
			//e.printStackTrace();??????????//ThrowDemo?e?=?new?ThrowDemo(s),初始化自定義異常，追溯并打印本類中該異常的錯(cuò)誤源頭
			//System.out.println();
			System.out.println("step03：接收test01中的拋出throw，匹配是ThrowDemo對(duì)象，到達(dá)test02?Catch?塊");
			RuntimeException?excption01?=?new?RuntimeException("test02中runtimeException中的catch塊");
			excption01.initCause(e);??//initCause(?throwable?cause)?即參數(shù)為可拋出異常的對(duì)象，ThrowDemo?e繼承Exception父類，即也屬于throwable類
			//如果沒有.initCause(?throwable?cause)，即沒有定義causeby源頭異常/起始異常---異常鏈，printStackTrace的時(shí)候就不能打印cause?by
			throw?excption01;?//拋出異常exception01??
		}
	}
	public?static?void?main(String[]?args)?{
		/*
		?*??TODO??
		?*??test01拋出異常
		?*??test02調(diào)用有拋出異常的方法，對(duì)該方法進(jìn)行try異常捕獲catch,并且包裝成運(yùn)行時(shí)異常，繼續(xù)拋出
		?*??main方法，調(diào)用test02方法，嘗試捕獲test02的異常
		?*/
		ThrowDemoTest?t01=new?ThrowDemoTest();
		try{t01.test02();
		}catch(Exception?e){
			System.out.println("step04:到達(dá)main?Catch?塊，catch接收throw出來的excption01");
			e.printStackTrace();
		}
		
		
		
	}

}

結(jié)果result:

step01:準(zhǔn)備運(yùn)行test01

step02:Reach test01，new ThrowDemo 初始化函數(shù)構(gòu)造器--》ThrowDemo異常對(duì)象，并拋出throw e

Here is ThrowDemo(String s)

step03：接收test01中的拋出throw，匹配是ThrowDemo對(duì)象，到達(dá)test02 Catch 塊

step04:到達(dá)main Catch 塊，catch接收throw出來的excption01

java.lang.RuntimeException: test02中runtimeException中的catch塊

at com.imooc.season3.ThrowDemoTest.test02(ThrowDemoTest.java:18)

at com.imooc.season3.ThrowDemoTest.main(ThrowDemoTest.java:32)

Caused by: com.imooc.season3.ThrowDemo: test01拋出異常

at com.imooc.season3.ThrowDemoTest.test01(ThrowDemoTest.java:7)

at com.imooc.season3.ThrowDemoTest.test02(ThrowDemoTest.java:13)