Java custom Exception

Java custom Exception

Here we will summarize the Java Exception and implement a custom Exception class.

Summary:

1. Throwable objects can be divided into two types: Error (indicating Compilation Time and system errors) and Exception (Exceptions thrown during Java class libraries, user methods, and runtime faults ).
2. Exception is divided into two types: checked exceptions (such as IOException and SQLException. Exceptions that need to be forcibly checked during compilation must be handled using the try, catch, and finally keywords during compilation; otherwise, an error will be reported .); Runtime exceptions (such as ArithmeticException, ClassCastException, IllegalArgumentException, IndexOutOfBoundsException, and NullPointerException. The compiler does not check for such exceptions .)
3. Best practices for exception handling in Java programming [4]:
   • Checktype exceptions are used for recoverable errors and non-checktype errors are used for programming errors.
   • Close or release resources in finally Blocks
   • Include the cause of the exception in the stack trace.
   • Always provide meaningful and complete information about exceptions
   • Avoid excessive use of Check type exceptions
   • Convert a checkpoint exception to an exception during running
   • Remember, exceptions are expensive for performance.
   • Avoid empty catch Blocks
   • Usage standard exception
   • Record exceptions thrown by any method
   • Differences between checked exceptions and runtime exceptions:
     • The checked exceptions need to be handled by yourself, and the runtime exceptions do not need to be
     • The checked Exception is the direct subclass of Exception, and the runtime Exception is the subclass of RuntimeException.
     • Most of the checked exceptions are errors during programming, and the failure rate during running is high.
     • Best practices for avoiding NullPointerException [5]:
       • Call the equals () and equalsIgnoreCase () methods ["hello". equals (objString)] with known string objects )];
       • If the return values of the valueOf () and toString () methods are the same, use the valueOf () method instead of the toString () method [when the null object calls toString () an NullPointerException exception is thrown when the method is called. When the valueOf () method is called, a "null" encapsulation class is returned ];
       • Use null-safe methods and libraries such as eg, StringUtils. isBlank (), isNumeric (), and isWhiteSpace ];
       • The return value of a method call should return an empty set or an empty array to avoid the return of null [Collections. EMPTY_LIST, Collections. EMPTY_SET and Collections. EMPTY_MAP ];
       • The @ NotNull and @ Nullable annotations are used to indicate whether null may occur;
       • Avoid unnecessary automatic packing and unpacking in the code. [avoid receiving a return value of null for int a. Use Integer a instead of null ];
       • Follow the contract and use a reasonable default value [the caller can make a clear decision by defining what can be blank and what cannot be blank .];
       • When using a database to store objects, You need to define whether to allow a field to be null. In this way, the database's own mechanism can check whether it is null to avoid invalid blank fields after the program calls it.
       • Use null to encapsulate the Null class of the object.

         Customize an Exception class:

         ProjectNameException. java content is as follows:

         ?

         package com.trianlge23.projectname.exception;public class ProjectNameException extends Throwable {private static final long serialVersionUID = 8093803025939797139L;//exception codeprivate int exceptionCode;//exception detailed messageprivate String detailMsg;public ProjectNameException(int exceptionCode, String extraMsg) {super();this.setDetailMsg(exceptionCode);this.setExtraMsg(extraMsg);}public ProjectNameException(int exceptionCode) {super();this.setDetailMsg(exceptionCode);}//notice: we do not offer the set method to set the excption code.public int getExceptionCode() {return exceptionCode;}//if there has no extra message for this excption code, init it.private void setDetailMsg(int exceptionCode) {this.exceptionCode = exceptionCode;if (ProjectNameExceptionCode.EXCEPTION_CODE_MAP.containsKey(exceptionCode)) {this.detailMsg = ProjectNameExceptionCode.EXCEPTION_CODE_MAP.get(exceptionCode);} else {this.detailMsg = ProjectNameExceptionCode.EXCEPTION_CODE_MAP.get(ProjectNameExceptionCode.PROJECTNAME_EXCEPTION_CODE_NOT_FOUND);}}//if there has extra message for this exception code, add it.private void setExtraMsg(String extraMsg) {this.detailMsg += ProjectNameExceptionCode.EXTRA_EXCEPTION_MSG_SPLITER+ extraMsg;}//override the super class method getMessage()@Overridepublic String getMessage() {return this.detailMsg;}}

         
         

         The content of ProjectNameExceptionCode. java is as follows:

         ?

         package com.triangle23.projectname.exception;import java.util.HashMap;import java.util.Map;public class ProjectNameExceptionCode {//the separator between default message and extra message of exception.public static final String EXTRA_EXCEPTION_MSG_SPLITER = ": ";//the map stores the exception code and exception messagepublic static Map
                  
                    EXCEPTION_CODE_MAP;public static final int PROJECTNAME_EXCEPTION_CODE_NOT_FOUND = 1;static {EXCEPTION_CODE_MAP = new HashMap
                   
                    ();EXCEPTION_CODE_MAP.put(PROJECTNAME_EXCEPTION_CODE_NOT_FOUND,"[PROJECTNAME Exception] Not found exception code.");}}
                   
                  

         
         
         

         
         

         References:

         1. JDK1.7 API: http://docs.oracle.com/javase/7/docs/api/

         2. Java programming ideas (version 4)

         3. Valid Java

         4. Exception Handling Java Best Practices:
         Http://javarevisited.blogspot.com/2013/03/0-exception-handling-best-practices-in-Java-Programming.html

         5. Java Tips and Best practices to avoid NullPointerException:
         Http://javarevisited.blogspot.com/2013/05/java-tips-and-best-practices-to-avoid-nullpointerexception-program-application.html

         
         

         Note:

         If you have any mistakes, please correct them. You are welcome to discuss them and give us some guidance.

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