Clojure 学习入门（17）—— 异常处理

异常处理 
Clojure代码里面抛出来的异常都是运行时异常。当然从Clojure代码里面调用的java代码还是可能抛出那种需要检查的异常的。

try - catch - finally 以及throw 提供了和java里面类似的功能。

try、catch、throw、finally： 

user=> (try (throw (Exception. "error")) (finally (println "final")))
final
Exception error  user/eval310 (NO_SOURCE_FILE:1)

user=> (try (/ 3 0) (catch Exception e (println e)))
#<ArithmeticException java.lang.ArithmeticException: Divide by zero>
nil

assert： 
它测试一个表达式， 如果这个表达式的值为false的话，它会抛出异常。 

user=> (assert true)
nil
user=> (assert false)
AssertionError Assert failed: false  user/eval317 (NO_SOURCE_FILE:1)
user=> (assert nil)
AssertionError Assert failed: nil  user/eval319 (NO_SOURCE_FILE:1)
user=> (assert 0)
nil
user=> (assert [1 2 3])
nil
user=> (assert "foo")
nil

clojure 完整示例：

(ns helloclojure.myexception)

(defn exception_test1 []
  (try (throw (Exception. "--error--"))
    (finally (println "final"))
    ))

(defn exception_test2 []
  (try (/ 3 0) 
    (catch Exception e (println "error: " e))
    ))

(defn exception_test3 [cls]
  (try (Class/forName cls) true
    (catch ClassNotFoundException e false))
  )

;(exception_test1)
(exception_test2)   ; error:  #<ArithmeticException java.lang.ArithmeticException: Divide by zero>
;(exception_test3 helloclojure.myexception)


(assert true)        

;(assert false)
;(try (assert false)
;  (catch Exception e (println "error" e))
;  (finally (println 'finally)))

;(assert nil)

(assert [1 2 3])

(assert "foo")

(assert 0)

(print 'end)