checked-exceptions | 易学教程

Checked exceptions thrown from within lambda expressions

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问题 Can you please explain why checked exceptions have to be caught from within lambda expressions? In other words, why does the following code not compile... public void doSomething(ObjectInputStream istream) throws IOException { // The read method throws an IOException. IntStream.range(0, 10).forEach(i -> someList.add(read(istream))); } but this one will? public void doSomething(ObjectInputStream istream) throws IOException { IntStream.range(0, 10).forEach(i -> { try { // The read method throws

How to wrap checked exceptions but keep the original runtime exceptions in Java

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问题 I have some code that might throw both checked and runtime exceptions. I'd like to catch the checked exception and wrap it with a runtime exception. But if a RuntimeException is thrown, I don't have to wrap it as it's already a runtime exception. The solution I have has a bit overhead and isn't "neat": try { // some code that can throw both checked and runtime exception } catch (RuntimeException e) { throw e; } catch (Exception e) { throw new RuntimeException(e); } Any idea for a more elegant

Why is catching checked exceptions allowed for code that does not throw exceptions?

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问题 In Java, methods that throw checked exceptions (Exception or its subtypes - IOException, InterruptedException, etc) must declare throws statement: public abstract int read() throws IOException; Methods that do not declare throws statement can't throw checked exceptions. public int read() { // does not compile throw new IOException(); } // Error: unreported exception java.io.IOException; must be caught or declared to be thrown But catching checked exceptions in safe methods is still legal in

Checked vs. Unchecked Exceptions in Service Layer

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问题 I work on a project with a legacy service layer that returns null in many places if a requested record does not exist, or cannot be accessed due to the caller not being authorized. I am talking about specific records requested by ID. For instance, something like: UserService.get(userId); I have recently pushed to have this API changed, or supplemented with a new API that throws exceptions instead. The debate over checked vs unchecked exceptions has ensued. Taking a note from the designers of

Why is “throws Exception” necessary when calling a function?

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class throwseg1 { void show() throws Exception { throw new Exception("my.own.Exception"); } void show2() throws Exception // Why throws is necessary here ? { show(); } void show3() throws Exception // Why throws is necessary here ? { show2(); } public static void main(String s[]) throws Exception // Why throws is necessary here ? { throwseg1 o1 = new throwseg1(); o1.show3(); } } Why compiler reports that methods show2() , show3() , and main() have unreported exception Exception that must be caught or declared to be thrown when I remove throws Exception from these methods? Jomoos In Java, as

Wrapping a checked exception into an unchecked exception in Java?

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问题 I have this factory method in java: public static Properties getConfigFactory() throws ClassNotFoundException, IOException { if (config == null) { InputStream in = Class.forName(PACKAGE_NAME).getResourceAsStream(CONFIG_PROP); config = new Properties(); config.load(in); } return config; } And I want to transform the two checked exceptions into unchecked exceptions. What is the best way to go about this? Should I just catch the exception and throw a new RuntimeException using the caught

How do I fix a compilation error for unhandled exception on call to Thread.sleep()?

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I am new to Java and kind of new to programming (I know diving straight into Java probably wasn't the greatest idea.) and I've been getting an error consistently no matter how I try to add a pause in my program. I am doing a simple counting program and want to add a one second delay between each number here is the code I have so far: import java.lang.*; public class Counter { public static void main(String[]args) { int i; for (i = 0; i <= 10; i++) { Thread.sleep(1000); System.out.println(i); } System.out.println("You can count to ten."); } } The call to Thread.sleep() won't compile. The javac

Checked vs Unchecked exception

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I've studied that: With an unchecked exception, however, the compiler doesn't force client programmers either to catch the exception or declare it in a throws clause. In fact, client programmers may not even know that the exception could be thrown. eg, StringIndexOutOfBoundsException thrown by String's charAt() method. what its mean? according to that code there is no need to put try catch block in code, but i've seen compiler forces to put the code in try catch block. I'm very confused what they are exactly? Unchecked exceptions are those that extend RuntimeException class. Compiler will

Differences between Runtime/Checked/Unchecked/Error/Exception

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What are the Runtime exceptions and what are Checked/Unchecked Exceptions and difference between Error/Exception.Why these many types? Instead Java may simply follow a simple design(just try/catch all types) to handle an abnormal condition in a program? Throwable is at the top off all exceptions. Underneath Throwable you have Error and Exception. Underneath Exception you have RuntimeException. Java has two types of exceptions - checked and unchecked. Checked exceptions are enforced by the compiler (you have to declare them in the throws clause and catch them eventually). Unchecked exceptions

Java 8: Mandatory checked exceptions handling in lambda expressions. Why mandatory, not optional?

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I'm playing with the new lambda features in Java 8, and found that the practices offered by Java 8 are really useful. However, I'm wondering is there a good way to make a work-around for the following scenario. Suppose you have an object pool wrapper that requires some kind of a factory to fill the object pool, for example (using java.lang.functions.Factory ): public class JdbcConnectionPool extends ObjectPool<Connection> { public ConnectionPool(int maxConnections, String url) { super(new Factory<Connection>() { @Override public Connection make() { try { return DriverManager.getConnection(url)