ch13 EXCEPTION HANDLING

13-1 Introduction

An exception is an object that represents an error or a condition that prevents execution from proceeding normally

13-2 Exception-Handling Overview

參考 p.456 程式 Listing 13.1 Quotient.java

參考 p.456 程式 Listing 13.2 QuotientWithIf.java

參考 p.457 程式 Listing 13.3 QuotientWithException.java 

throw new ArithmeticException("Divisor cannot be zero");

try {
可能發生例外的程式碼
} catch (ArithmeticException ex) {
發生ArithmeticException例外時
} catch (Exception ex) {
發生其他例外時
}

13-3 Exception-Handling Advantages

參考 p.459 程式 Listing 13.4 QuotientWithMethod.java

參考 p.460 程式 Listing 13.5 FileNotFoundExceptionDemo.java

參考 p.460 程式 Listing 13.6 InputMismatchExceptionDemo.java

13-4 Exception Types

p.461 Figure 13.1 Exceptions thrown are instances of the classes shown in this diagram, or of subclasses of one of these classes

p.462 TABLE 13.1 Examples of Subclasses of Error

class 可能發生的原因
LinkageError Class 的介面更改，無法連結
VirtualMachineError 系統錯誤（記憶體不夠等）

p.462 TABLE 13.2 Examples of Subclasses of Exception

class 可能發生的原因
ClassNotFoundException Class 找不到
IOException 讀取或寫入資料錯誤

p.462 TABLE 13.3 Examples of Subclasses of RuntimeException

class 可能發生的原因
ArithmeticException 計算時錯誤（如除以0）
NullPointerException 物件變數沒有 new ，直接存取欄位或方法
IndexOutOfBoundsException 陣列索引超過下限或上限
IllegalArgumentException 傳遞給方法的參數不正確 
int number = Integer.MAX_VALUE + 1;
System.out.println(number);

13-5 More on Exception Handling

p.463 Figure 13.2 Exception handling in Java consists of declaring exceptions, throwing exceptions, and catching and processing exceptions

13-5-1 Declaring Exceptions

public void myMethod() throws IOException

public void myMethod() throws Exception1, Exception2, ..., ExceptionN

13-5-2 Throwing Exceptions

throw new IllegalArgumentException("Wrong Argument");

13-5-3 Catching Exceptions

try {
statements; // Statements that may throw exceptions
}
catch (Exception1 exVar1) {
handler for exception1;
}
catch (Exception2 exVar2) { 
handler for exception2;
}
catch (ExceptionN exVar3) {
handler for exceptionN;
}

p.465 Figure 13.3 If an exception is not caught in the current method, it is passed to its caller. The process is repeated until the exception is caught or passed to the main method.

p.466 Note 多個 exception 的 catch 順序

p.466 Note 必須處理的 exception

只要不是 error 或 RuntimeException ,必須自己處理或另外丟給別人處理

13-5-4 Getting Information from Exceptions

p.466 Figure 13.4 Throwable is the root class for all exception objects.

參考 p.467 程式 Listing 13.7 TestException.java

13-5-5 Example: Declaring, Throwing, and Catching Exceptions

參考 p.468 程式 Listing 13.8 CircleWithException.java

參考 p.468 程式 Listing 13.9 TestCircleWithException.java

13-6 The finally Clause

finally 句子一定會被執行

參考 p.470 程式 Listing 13.10 FinallyDemo.java

13-7 When to Use Exceptions

try {
	System.out.println(refVar.toString());
}
catch (NullPointerException ex) {
	System.out.println("refVar is null");
}

if (refVar != null)
	System.out.println(refVar.toString());
else
	System.out.println("refVar is null");

13-8 Rethrowing Exceptions

try {
	statements;
}
catch (TheException ex) {
	perform operations before exits;
	throw ex;
}

13-9 Chained Exceptions

參考 p.472 程式 Listing 13.11 ChainedExceptionDemo.java

13-10 Creating Custom Exception Classes

參考 p.473 程式 Listing 13.12 InvalidRadiusException.java