Java从入门到实战之（29）Java 异常处理之练习
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内容图文
1、异常处理的方法
使用 System 类的 System.err.println() 来展示异常的处理方法?
class ExceptionDemo
{
public static void main(String[] args) {
try {
throw new Exception("My Exception");
} catch (Exception e) {
System.err.println("Caught Exception");
System.err.println("getMessage():" + e.getMessage());
System.err.println("getLocalizedMessage():" + e.getLocalizedMessage());
System.err.println("toString():" + e);
System.err.println("printStackTrace():");
e.printStackTrace();
}
}
}
结果：
"C:\Program Files\Java\jdk1.8.0_221\bin\java.exe" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2019.3.3\lib\idea_rt.jar=60857:C:\Program Files\JetBrains\IntelliJ IDEA 2019.3.3\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_221\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\rt.jar;C:\app\FlinkUdf\target\test-classes;C:\Users\defaultuser0\.m2\repository\junit\junit\4.11\junit-4.11.jar;C:\Users\defaultuser0\.m2\repository\org\hamcrest\hamcrest-core\1.3\hamcrest-core-1.3.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-table-api-java-bridge_2.11\1.11.1\flink-table-api-java-bridge_2.11-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-table-api-java\1.11.1\flink-table-api-java-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-java\1.11.1\flink-java-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\org\apache\commons\commons-lang3\3.3.2\commons-lang3-3.3.2.jar;C:\Users\defaultuser0\.m2\repository\org\apache\commons\commons-math3\3.5\commons-math3-3.5.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-streaming-java_2.11\1.11.1\flink-streaming-java_2.11-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-runtime_2.11\1.11.1\flink-runtime_2.11-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-queryable-state-client-java\1.11.1\flink-queryable-state-client-java-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-hadoop-fs\1.11.1\flink-hadoop-fs-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\commons-io\commons-io\2.4\commons-io-2.4.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-shaded-netty\4.1.39.Final-11.0\flink-shaded-netty-4.1.39.Final-11.0.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-shaded-jackson\2.10.1-11.0\flink-shaded-jackson-2.10.1-11.0.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-shaded-zookeeper-3\3.4.14-11.0\flink-shaded-zookeeper-3-3.4.14-11.0.jar;C:\Users\defaultuser0\.m2\repository\commons-cli\commons-cli\1.3.1\commons-cli-1.3.1.jar;C:\Users\defaultuser0\.m2\repository\com\typesafe\akka\akka-actor_2.11\2.5.21\akka-actor_2.11-2.5.21.jar;C:\Users\defaultuser0\.m2\repository\com\typesafe\config\1.3.3\config-1.3.3.jar;C:\Users\defaultuser0\.m2\repository\org\scala-lang\modules\scala-java8-compat_2.11\0.7.0\scala-java8-compat_2.11-0.7.0.jar;C:\Users\defaultuser0\.m2\repository\com\typesafe\akka\akka-stream_2.11\2.5.21\akka-stream_2.11-2.5.21.jar;C:\Users\defaultuser0\.m2\repository\org\reactivestreams\reactive-streams\1.0.2\reactive-streams-1.0.2.jar;C:\Users\defaultuser0\.m2\repository\com\typesafe\ssl-config-core_2.11\0.3.7\ssl-config-core_2.11-0.3.7.jar;C:\Users\defaultuser0\.m2\repository\com\typesafe\akka\akka-protobuf_2.11\2.5.21\akka-protobuf_2.11-2.5.21.jar;C:\Users\defaultuser0\.m2\repository\com\typesafe\akka\akka-slf4j_2.11\2.5.21\akka-slf4j_2.11-2.5.21.jar;C:\Users\defaultuser0\.m2\repository\org\clapper\grizzled-slf4j_2.11\1.3.2\grizzled-slf4j_2.11-1.3.2.jar;C:\Users\defaultuser0\.m2\repository\com\github\scopt\scopt_2.11\3.5.0\scopt_2.11-3.5.0.jar;C:\Users\defaultuser0\.m2\repository\org\xerial\snappy\snappy-java\1.1.4\snappy-java-1.1.4.jar;C:\Users\defaultuser0\.m2\repository\com\twitter\chill_2.11\0.7.6\chill_2.11-0.7.6.jar;C:\Users\defaultuser0\.m2\repository\com\twitter\chill-java\0.7.6\chill-java-0.7.6.jar;C:\Users\defaultuser0\.m2\repository\org\lz4\lz4-java\1.6.0\lz4-java-1.6.0.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-shaded-guava\18.0-11.0\flink-shaded-guava-18.0-11.0.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-streaming-java_2.11\1.11.1\flink-streaming-java_2.11-1.11.1-tests.jar;C:\Users\defaultuser0\.m2\repository\org\slf4j\slf4j-api\1.7.15\slf4j-api-1.7.15.jar;C:\Users\defaultuser0\.m2\repository\com\google\code\findbugs\jsr305\1.3.9\jsr305-1.3.9.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\force-shading\1.11.1\force-shading-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-table-planner-blink_2.11\1.11.1\flink-table-planner-blink_2.11-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-table-api-scala_2.11\1.11.1\flink-table-api-scala_2.11-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-table-api-scala-bridge_2.11\1.11.1\flink-table-api-scala-bridge_2.11-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-table-runtime-blink_2.11\1.11.1\flink-table-runtime-blink_2.11-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\org\codehaus\janino\janino\3.0.9\janino-3.0.9.jar;C:\Users\defaultuser0\.m2\repository\org\codehaus\janino\commons-compiler\3.0.9\commons-compiler-3.0.9.jar;C:\Users\defaultuser0\.m2\repository\org\apache\calcite\avatica\avatica-core\1.16.0\avatica-core-1.16.0.jar;C:\Users\defaultuser0\.m2\repository\org\reflections\reflections\0.9.10\reflections-0.9.10.jar;C:\Users\defaultuser0\.m2\repository\org\javassist\javassist\3.19.0-GA\javassist-3.19.0-GA.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-streaming-scala_2.11\1.11.1\flink-streaming-scala_2.11-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-scala_2.11\1.11.1\flink-scala_2.11-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\org\scala-lang\scala-reflect\2.11.12\scala-reflect-2.11.12.jar;C:\Users\defaultuser0\.m2\repository\org\scala-lang\scala-library\2.11.12\scala-library-2.11.12.jar;C:\Users\defaultuser0\.m2\repository\org\scala-lang\scala-compiler\2.11.12\scala-compiler-2.11.12.jar;C:\Users\defaultuser0\.m2\repository\org\scala-lang\modules\scala-xml_2.11\1.0.5\scala-xml_2.11-1.0.5.jar;C:\Users\defaultuser0\.m2\repository\org\scala-lang\modules\scala-parser-combinators_2.11\1.0.4\scala-parser-combinators_2.11-1.0.4.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-table-common\1.11.1\flink-table-common-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-core\1.11.1\flink-core-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-annotations\1.11.1\flink-annotations-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-metrics-core\1.11.1\flink-metrics-core-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\com\esotericsoftware\kryo\kryo\2.24.0\kryo-2.24.0.jar;C:\Users\defaultuser0\.m2\repository\com\esotericsoftware\minlog\minlog\1.2\minlog-1.2.jar;C:\Users\defaultuser0\.m2\repository\org\objenesis\objenesis\2.1\objenesis-2.1.jar;C:\Users\defaultuser0\.m2\repository\org\apache\commons\commons-compress\1.20\commons-compress-1.20.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-shaded-asm-7\7.1-11.0\flink-shaded-asm-7-7.1-11.0.jar;C:\Users\defaultuser0\.m2\repository\com\alibaba\fastjson\1.2.73\fastjson-1.2.73.jar;C:\Users\defaultuser0\.m2\repository\org\slf4j\slf4j-log4j12\1.7.7\slf4j-log4j12-1.7.7.jar;C:\Users\defaultuser0\.m2\repository\log4j\log4j\1.2.17\log4j-1.2.17.jar;C:\Users\defaultuser0\.m2\repository\net\sf\json-lib\json-lib\2.4\json-lib-2.4-jdk15.jar;C:\Users\defaultuser0\.m2\repository\commons-beanutils\commons-beanutils\1.8.0\commons-beanutils-1.8.0.jar;C:\Users\defaultuser0\.m2\repository\commons-collections\commons-collections\3.2.1\commons-collections-3.2.1.jar;C:\Users\defaultuser0\.m2\repository\commons-lang\commons-lang\2.5\commons-lang-2.5.jar;C:\Users\defaultuser0\.m2\repository\commons-logging\commons-logging\1.1.1\commons-logging-1.1.1.jar;C:\Users\defaultuser0\.m2\repository\net\sf\ezmorph\ezmorph\1.0.6\ezmorph-1.0.6.jar;C:\Users\defaultuser0\.m2\repository\org\json\json\20180813\json-20180813.jar" Practice.Test1
Caught Exception
getMessage():My Exception
getLocalizedMessage():My Exception
toString():java.lang.Exception: My Exception
printStackTrace():
java.lang.Exception: My Exception
at Practice.Test1.main(Test1.java:11)
Process finished with exit code 0
2、多个异常处理（多个catch)
对异常的处理：
1，声明异常时，建议声明更为具体的异常，这样可以处理的更具体
2,对方声明几个异常，就对应几个catch块， 如果多个catch块中的异常出现继承关系，父类异常catch块放在最下面
class Demo
{
int div(int a,int b) throws ArithmeticException,ArrayIndexOutOfBoundsException//在功能上通过throws的关键字声明该功能可能出现问题
{
int []arr = new int [a];
System.out.println(arr[4]);//制造的第一处异常
return a/b;//制造的第二处异常
}
}
class ExceptionDemo
{
public static void main(String[]args) //throws Exception
{
Demo d = new Demo();
try
{
int x = d.div(4,0);//程序运行截图中的三组示例 分别对应此处的三行代码
//int x = d.div(5,0);
//int x = d.div(4,1);
System.out.println("x="+x);
}
catch (ArithmeticException e)
{
System.out.println(e.toString());
}
catch (ArrayIndexOutOfBoundsException e)
{
System.out.println(e.toString());
}
catch (Exception e)//父类 写在此处是为了捕捉其他没预料到的异常 只能写在子类异常的代码后面
//不过一般情况下是不写的
{
System.out.println(e.toString());
}
System.out.println("Over");
}
}
结果：
java.lang.ArrayIndexOutOfBoundsException: 4 Over
3、Finally的用法
Java 中的 Finally 关键一般与try一起使用，在程序进入try块之后，无论程序是因为异常而中止或其它方式返回终止的，finally块的内容一定会被执行 。
以下实例演示了如何使用 finally 通过 e.getMessage() 来捕获异常（非法参数异常）？
public class ExceptionDemo2 {
public static void main(String[] argv) {
new ExceptionDemo2().doTheWork();
}
public void doTheWork() {
Object o = null;
for (int i=0; i<5; i++) {
try {
o = makeObj(i);
}
catch (IllegalArgumentException e) {
System.err.println
("Error: ("+ e.getMessage()+").");
return;
}
finally {
System.err.println("都已执行完毕");
if (o==null)
System.exit(0);
}
System.out.println(o);
}
}
public Object makeObj(int type)
throws IllegalArgumentException {
if (type == 1)
throw new IllegalArgumentException
("不是指定的类型： " + type);
return new Object();
}
}
结果：
都已执行完毕 java.lang.Object@7852e922 Error: (不是指定的类型：1). 都已执行完毕
4、使用catch处理异常
使用 catch 来处理异常的方法？
public class Main {
public static void main (String args[]) {
int array[]={20,20,40};
int num1=15,num2=10;
int result=10;
try{
result = num1/num2;
System.out.println("结果为 " +result);
for(int i =5;i >=0; i--) {
System.out.println ("数组的元素值为 " +array[i]);
}
}
catch (Exception e) {
System.out.println("触发异常 : "+e);
}
}
}
结果：
结果为 1 触发异常 : java.lang.ArrayIndexOutOfBoundsException: 5
5、多线程异常处理
package Practice;
/**
* @program: FlinkUdf
* @description: 文件目录
* @author: BigData
* @create: 2020-11-09 14:19
**/
class MyThread extends Thread
{
@Override
public void run() {
System.out.println("Throwing in " +"MyThread");
throw new RuntimeException();
}
}
public class Test1 {
public static void main(String[] args) {
MyThread t=new MyThread();
t.start();
try {
Thread.sleep(1000);
}
catch (Exception x)
{
System.out.println("Caught it" + x);
}
}
}
结果：
"C:\Program Files\Java\jdk1.8.0_221\bin\java.exe" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2019.3.3\lib\idea_rt.jar=61117:C:\Program Files\JetBrains\IntelliJ IDEA 2019.3.3\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_221\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\resources.jar;C:\Program 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Practice.Test1
Exception in thread "Thread-0" java.lang.RuntimeException
at Practice.MyThread.run(Test1.java:13)
Throwing in MyThread
Process finished with exit code 0
6、获取异常的堆栈信息
如何使用异常类的 printStack() 方法来获取堆栈信息？
public class Main{
public static void main (String args[]){
int array[]={20,20,40};
int num1=15,num2=10;
int result=10;
try{
result = num1/num2;
System.out.println("The result is" +result);
for(int i =5; i>=0; i--) {
System.out.println("The value of array is" +array[i]);
}
}
catch (Exception e) {
e.printStackTrace();
}
}
}
结果：
The result is1
java.lang.ArrayIndexOutOfBoundsException: 5
at testapp.Main.main(Main.java:28)
7、重载方法异常处理
public class Main {
double method(int i) throws Exception{
return i/0;
}
boolean method(boolean b) {
return !b;
}
static double method(int x, double y) throws Exception {
return x + y ;
}
static double method(double x, double y) {
return x + y - 3;
}
public static void main(String[] args) {
Main mn = new Main();
try{
System.out.println(method(10, 20.0));
System.out.println(method(10.0, 20));
System.out.println(method(10.0, 20.0));
System.out.println(mn.method(10));
}
catch (Exception ex){
System.out.println("exception occoure: "+ ex);
}
}
}
结果：
30.0 27.0 27.0 exception occoure: java.lang.ArithmeticException: / by zero
8、链式异常
public class Main {
public static void main (String args[])throws Exception {
int n=20,result=0;
try{
result=n/0;
System.out.println("结果为"+result);
}
catch(ArithmeticException ex){
System.out.println("发算术异常: "+ex);
try {
throw new NumberFormatException();
}
catch(NumberFormatException ex1) {
System.out.println("手动抛出链试异常 : "+ex1);
}
}
}
}
结果：
发算术异常: java.lang.ArithmeticException: / by zero 手动抛出链试异常 : java.lang.NumberFormatException
9、自定义异常
通过继承 Exception 来实现自定义异常？
class WrongInputException extends Exception { // 自定义的类
WrongInputException(String s) {
super(s);
}
}
class Input {
void method() throws WrongInputException {
throw new WrongInputException("Wrong input"); // 抛出自定义的类
}
}
class TestInput {
public static void main(String[] args){
try {
new Input().method();
}
catch(WrongInputException wie) {
System.out.println(wie.getMessage());
}
}
}
结果：
Wrong input
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