java - 将parseUnsignedInt移植到java1.7

Question

我使用的是 java1.8，它有 parseUnsignedInt()。我被告知我们必须使用 java1.7，因为它在系统上。我以为我可以移植 java.lang.Interger.java、java.lang.Long.java 和 java.lang.annotation.Native.java 函数并使用我的代码进行编译。这允许代码编译无误。运行时出现以下错误:

Exception in thread "Thread-6" java.lang.NoSuchMethodError: java.lang.Integer.parseUnsignedInt(Ljava/lang/String;)I

eclipse 调试器似乎也找不到函数。我需要做什么才能让它正常工作？

Answer 1

parseUnsignedInt 方法是在 Java 1.8 中引入的，在它的 javadoc 中有记录(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 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。

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

有关安全性的详细信息(即为什么您不能将自己的 Integer 类放入 java.lang 包中)、否决此安全性的选项以及您不应该(或更好 - 为什么不允许)的原因, 请参阅 Why I am able to re-create java.lang package and classes? 中的选定答案

因此，您必须在自己的包中实现自己的类:

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，让所有调用者调用 com.yourname.IntCompatUtilities.parseUnsignedInt(...)