How do checked and unchecked exceptions differ in Java?

Explains Java's catch-or-declare rule and turns exception choice into a recoverability and API-contract decision rather than a universal slogan.

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A checked exception is an exception the compiler requires a method to catch or declare with throws. Exceptions under RuntimeException, and errors under Error, are unchecked and have no catch-or-declare requirement. Checked exceptions make a failure part of the method's compile-time contract. I consider them when a caller can reasonably anticipate and recover from a specific condition. I use unchecked exceptions for programming errors, violated preconditions, or failures that callers usually cannot handle meaningfully at each layer.

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Exception hierarchy, compiler enforcement, caller responsibility, recoverability, and API evolution.

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The language distinction is mechanical, while the design choice depends on what a caller can reasonably do with the failure.
A checked exception is an exception the compiler requires a method to catch or declare with throws. Exceptions under RuntimeException, and errors under Error, are unchecked and have no catch-or-declare requirement. Checked exceptions make a failure part of the method's compile-time contract. I consider them when a caller can reasonably anticipate and recover from a specific condition. I use unchecked exceptions for programming errors, violated preconditions, or failures that callers usually cannot handle meaningfully at each layer.
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Saying checked exceptions occur at compile time.
Catching a checked exception and ignoring it.
Declaring throws Exception everywhere.
Treating every external failure as automatically checked or unchecked.

How do checked and unchecked exceptions differ in Java?

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