[英]Clojure and Java interoperation: Java.math.BigInteger
我有一個輸出為BigInteger的clojure代碼。
(ns com.domain.tiny
(:gen-class
:name com.domain.tiny
:methods [#^{:static true} [binomial [int int] java.math.BigInteger]]))
(defn binomial
"Calculate the binomial coefficient."
[n k]
(let [a (inc n)]
(loop [b 1
c 1]
(if (> b k)
c
(recur (inc b) (* (/ (- a b) b) c))))))
(defn -binomial
"A Java-callable wrapper around the 'binomial' function."
[n k]
(binomial n k))
(defn -main []
(println (str "(binomial 5 3): " (binomial 5 3)))
(println (str "(binomial 10042 111): " (binomial 10042 111)))
)
單獨執行它,我可以毫無問題地得到結果:
(binomial 5 3): 10
(binomial 10042 111):
4906838957506814494663377752836616342 ...
48178314846156008309671682804824359157818666487159757179543983405334334410427200
我可以使用lein uberjar
生成jar文件。 試圖從Java中使用它,我提出了這個代碼。
import com.domain.tiny;
import java.math.BigInteger;
public class Hello
{
public static void main(String[] args) {
BigInteger res = tiny.binomial(5, 3);
System.out.println("(binomial 5 3): " + res);
res = tiny.binomial(10042, 111);
System.out.println("(binomial 10042, 111): " + res);
}
}
不幸的是,我得到了例外。
Exception in thread "main" java.lang.ClassCastException: java.lang.Long cannot be cast
to java.math.BigInteger
at com.domain.tiny.binomial(Unknown Source)
at Hello.main(Hello.java:11)
如何為Java.Math.BigInteger互操作clojure和Java? 我可以使用:methods [#^{:static true} [binomial [int int] double]]))
和double res = tiny.binomial(10042, 111);
但不是BigInteger。
這是我獲取jar並執行java的步驟。
lein new com.domain.tiny
copy the tiny.clj in com.domain
lein deps
lein uberjar
javac -cp .:com.domain.tiny-1.0.0-SNAPSHOT-standalone.jar Hello.java
java -cp .:com.domain.tiny-1.0.0-SNAPSHOT-standalone.jar Hello
clojure代碼復制自: 從java調用clojure
返回值應該是clojure.lang.BigInt。
:methods [#^{:static true} [binomial [int int] clojure.lang.BigInt]]))
(defn binomial
"Calculate the binomial coefficient."
[n k]
(let [a (inc n)]
(loop [b 1
c 1]
(if (> b k)
(bigint c) ;; <-- Without this code
;; java.lang.ClassCastException:
;; java.lang.Long cannot be cast to clojure.lang.BigInt occurs
(recur (inc b) (* (/ (- a b) b) c))))))
import clojure.lang.BigInt;
...
BigInt res = tiny.binomial(10042, 111);
System.out.println("(binomial 10042, 111): " + res.toString());
java -cp .:com.domain.tiny-1.0.0-SNAPSHOT-standalone.jar Hello
>>>
(binomial 5 3): 10
(binomial 10042 111): 49068389575068144946 … 27200
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