Question

我正在使用具有parseUnsignedInt()的java1.8。有人告诉我，我们必须使用java1.7，因为这已经在系统上了。我以为我可以只移植java.lang.Interger.java，java.lang.Long.java和java.lang.annotation.Native.java函数并用我的代码进行编译。这使代码可以正确编译。当我运行时，出现以下错误：

线程“ Thread-6”中的异常java.lang.NoSuchMethodError：java.lang.Integer.parseUnsignedInt（Ljava / lang / String;）I

eclipse调试器似乎也找不到该函数。我该怎么做才能使它正常工作？

Answer 1

parseUnsignedInt方法是Java 1.8引入的，因为它已在其Javadoc中记录（请注意 @since 1.8 ）：

/**
 * Parses the string argument as an unsigned decimal integer. The
 * characters in the string must all be decimal digits, except
 * that the first character may be an an ASCII plus sign {@code
 * '+'} ({@code '\u005Cu002B'}). The resulting integer value
 * is returned, exactly as if the argument and the radix 10 were
 * given as arguments to the {@link
 * #parseUnsignedInt(java.lang.String, int)} method.
 *
 * @param s   a {@code String} containing the unsigned {@code int}
 *            representation to be parsed
 * @return    the unsigned integer value represented by the argument in decimal.
 * @throws    NumberFormatException  if the string does not contain a
 *            parsable unsigned integer.
 * @since 1.8
 */
public static int parseUnsignedInt(String s) throws NumberFormatException {
    return parseUnsignedInt(s, 10);
}

但是JDK也包含源代码，因此您可以在自己的类中编写自己的parseUnsignedInt方法，如果Java 8许可证允许，则类似于Java 8中包含的实现。

请参见http://hg.openjdk.java.net/jdk8/jdk8/jdk/file/687fd7c7986d/src/share/classes/java/lang/Integer.java 661行ff

有关安全性的详细信息（即，为什么不能在java.lang包中放置自己的Integer类），否决该安全性的选项以及不应该这样做的原因（或更好的原因-不允许这样做），请参阅Why I am able to re-create java.lang package and classes?

中的选定答案

因此，您将必须在自己的程序包中实现自己的类：

package com.yourname;

/*
 * Contains code from OpenJDK Java8, Copyright (c) 1994, 2013, Oracle and/or its affiliates.
 * TODO add more info from Oracle class comment here.
 */
public class IntCompatUtilities {

    public static int parseUnsignedInt(String s) throws NumberFormatException {
        return parseUnsignedInt(s,10);
    }

    public static int parseUnsignedInt(String s, int radix)
                throws NumberFormatException {

        //TODO content from OpenJDK 8's Integer.parseUnsignedInt(String,int) here.
        //instead of return parseInt(s, radix); change to return Integer.parseInt(s, radix);
        //instead of throw NumberFormatException.forInputString(s); throw new NumberFormatException(...)
   }
}

然后，让所有呼叫者都呼叫com.yourname.IntCompatUtilities.parseUnsignedInt(...)

将parseUnsignedInt移植到java1.7

1 个答案: