how to use exceptions java

method that does not exist to access a class. Java. lang. NullPointerException Null Pointer exception. This exception is thrown when the application tries to use null where the object is required. For example, call the instance method of the null object, access the attribute of the null object, calculate the length of the null object, and throw null using the throw statement.

What is an exceptionWhen the program runs, unexpected events occur that prevent the program from executing as expected by the programmer, which is an exception. When the exception occurs, is any program to fend for itself, immediately quit terminating, or output errors to the user? or in C language style: Use function return value as execution state?Java provides a better solution: exception handling mechan

try...catch ... Block handling: java //Checked异常必须被显式处理 try { FileInputStream fis = new FileInputStream("test.md"); } catch (FileNotFoundException e) { e.printStackTrace(); System.out.println("文件不存在！"); } If you do not know how to handle it, it is thrown in the method and handled by the caller at the top level: "' Javapublic static void Main (string[] args) throws FileNotFoundException {//Checked异常必须被显式处理//在main方法中抛出异常，交给JVM处理，JVM对

of exception thrown by the method. The runtime system starts with the method in which the exception occurred and then turns back to the method in the call stack until it finds the method that contains the appropriate exception handler and executes it. The runtime system terminates when the runtime system traverses the call stack without finding an appropriate exception handler. At the same time, it means the termination of the Java program. Any

that does not exist to access a class. Java. lang. NullPointerException Null Pointer exception. This exception is thrown when the application tries to use null where the object is required. For example, call the instance method of the null object, access the attribute of the null object, calculate the length of the null object, and throw null using the throw statement.

The Java exception handling mechanism mainly relies on five keywords: Try, catch, finally, throw, and throws. The try keyword is followed by a code block enclosed in curly brackets, or try block for short. Similarly: The following is also called the corresponding block. It can set the code that causes exceptions. Catch corresponds to the exception type and a code block, which indicates that the catch block

RuntimeException in Java, and Runtime_error is equivalent to the exception of non-runtimeexception types in Java.3 How to use exceptionsdeclaring a method throws an exception① syntax: throws (slightly)② why declare a method to throw an exception?Method throws an exception as important as the type of the method return value. If the method throws an exception and

Exceptions are errors that occur during the process of running a program, described in Java by classes, and objects to represent specific exceptions. Java distinguishes it as error and exception,error are errors that the program cannot handle, and exception is the error that the program can handle. Exception handling i

how to handle the exception or do not want to deal with it, but do not deal with the inappropriate, which is to throw the exception to the previous level of processing"); Throwing Exceptions again Throw e; } } public static void Printfile (String file) { try { ReadFile (file); catch (FileNotFoundException e) { E.printstacktrace (); } } public static void Main (string[] args) { Printfile ("D:/file"); } } The origin

display of external exceptions. 2. sometimes, when we encounter some verification or problems, we need to directly end the current request, then we can end the process by throwing a custom exception, if SpringMVC is used in your project, the controller is enhanced, you can use the @ ControllerAdvice annotation to write a controller enhancement class to intercept custom

return to the results of the calculation, do not consider what parameters are correct, whether it is legal (of course, can be forgiven, who have come here). But we should think about it as well as possible, so that the "signs" that could lead to the failure of the program are stifled in the cradle, so it is necessary to examine the legality of the parameters. One of the parameters of the execution parameter check thrown out of the illegal exception, which belongs to this method of abnormal cond

accessed.Java.lang.NoSuchMethodExceptionMethod has no exception. This exception is thrown when a non-existent method of a class is accessed.Java.lang.NullPointerExceptionNull pointer exception. This exception is thrown when an app tries to use null where the object is required. For example: Call an instance method of a Null object, access the properties of a null object, evaluate the length of a null object, throw null with a throw statement, and so

Document directory Java. lang. Throwable Java. lang. Error Java. lang. Exception Java. lang. RuntimeException Generally, exceptions in Java are divided into three types: Error: this exception is designed not to be captu

I. What is an exceptionAbnormal English words are exception, literal translation is the meaning of "accident, exception", that is, abnormal situation. In fact, exceptions are procedural errors in nature, including procedural logic errors and system errors. For example, the use of empty references, array subscript out of bounds, memory overflow errors, and so on, these are unexpected circumstances, deviating

is very helpful for debugging problems that result in a high layer exception, it is appropriate to use an exception chain. The high-level exception provides an access method (Throwable.getcause) to obtain the lower layer exception.6), each method throws the exception to have the document description. Use the @throws tag of Javadoc to record the conditions that throw each exception. If a method may throw mo

: JAVA_HOME =/home/jdk CLASSPATH = $ JAVA_HOME/jre/lib/tools. jar: $ JAVA_HOME/lib/dt. jar: $ JAVA_HOME/jre/lib/: $ JAVA_HOME/lib PATH = $ PATH: $ JAVA_HOME/bin Hello. class is generated using the JAVAC command. When java hello is used, the following message is still displayed: Exception in thread "main" java. lang. NoClassDefFoundError: XXX (wrong name: XXX) Solution prompt: (1) Add (current directory) to

Basic applications with exceptions in Java (1), Java applications ( In Java, we treat exceptions as an object. It is the introduction of the exception mechanism that makes our programs more robust. An exception indicates an abnormal condition or an error condition, which is

1:unchecked Exception (i.e. runtime exception) VS Check Exception (non-runtime exception)2: Run-time exception VS non-run-time exception?Non-runtime Exceptions: The claim captures that must be displayed in code are either placed in the Try{}catch () {} block or declared throws on the method to throw the exception, and the type belongs to the exception class and its subclasses .Run-time exception: do not need to be specifically stated , the General run

program may be running in a variety of unknown environment, and the programmer can not interfere with the user how to use the program he wrote, so the programmer should be prepared for such an unusual moment. This kind of anomaly has sqlexception, ioexception,classnotfoundexception and so on.How to handle Exceptions:There are two ways in which Java code processing can check for

exception handlingFor example:try{......}catch (Exception e) {throw new Exception (msg,e);Return "";}Mixed use of Java exception handling mechanisms and return values makes the exception handling part of the program "ugly" and difficult to understand. If there are many different exceptions, define a number of different excep