Oracle Java教程-有关字符自动装箱Java注释的可能错误 [英] Oracle java tutorial - possible error regarding Character autoboxing java comment

问题描述

我是JAVA的新手，目前正在学习Oracle教程泛型部分.我认为那里有一个错误，我想确保我没有记错.感谢您的反馈.

I'm new to JAVA, currently learning Oracle tutorial generics section. I think there is a mistake there, and I want to make sure I'm not wrong. I'll appreciate your feedback.

我在下面看到了以下解释 https://docs.oracle.com/javase/tutorial/java/generics/restrictions.html

I saw the following explanation at https://docs.oracle.com/javase/tutorial/java/generics/restrictions.html

对<整数，字符> p =新对<(8，'a');

Pair < Integer, Character > p = new Pair<>(8, 'a');

请注意，Java编译器自动将8装箱为Integer.valueOf(8)，将'a'装箱为Character('a'):

Note that the Java compiler autoboxes 8 to Integer.valueOf(8) and 'a' to Character('a'):

对<整数，字符> p =新对(<>)(Integer.valueOf(8)，新字符('a'));

Pair < Integer, Character > p = new Pair<>(Integer.valueOf(8), new Character('a'));

我认为这是一个错误，"a"实际上会自动装箱到 Character.valueOf('a').

I think this is a mistake and 'a' is actually auto-boxed to Character.valueOf('a').

我编写了以下程序来检查它.正如我以为泛型可能具有特殊的装箱方法，我尝试了泛型方法，常规方法和泛型类:

I wrote the following program to check it. as I thought maybe generics have special boxing, I tried generic method, regular method and generic class:

class TestCharacter<T>{
public <T> void check( T first, T second){
    System.out.println("values: " + first + "  " + second);
    System.out.println(first.equals(second));
    System.out.println( "first == second is " + (first == second) );
    System.out.println( "first == second is " + (first == Character.valueOf('a')) );
}
}

public class TestAutoBoxingIssue{

public static <T> void check1( T first, T second){
    System.out.println("values: " + first + "  " + second);
    System.out.println(first.equals(second));
    System.out.println( "first == second is " + (first == second) );
    System.out.println( "first == second is " + (first == Character.valueOf('a')) );
}
public static void check2( Character first, Character second){
    System.out.println("values: " + first + "  " + second);
    System.out.println(first.equals(second));
    System.out.println( "first == second is " + (first == second) );
    System.out.println( "first == second is " + (first == Character.valueOf('a')) );
}
public static void main(String[] args){
    char first = 'a';
    char second = 'a';
    System.out.println("generic method usage: ");
    check1( first, second );
    System.out.println("=============");

    System.out.println("regular method usage: ");
    check2( first, second );
    System.out.println("=============");

    TestCharacter<Character> t = new TestCharacter<>();
    System.out.println("generic class usage: ");
    t.check(first, second );
    System.out.println("=============");
}

}

输出为:

通用方法用法:值:一个真的第一==第二是真的

generic method usage: values: a a true first == second is true

常规方法用法:值:一个真的第一==第二是真的

regular method usage: values: a a true first == second is true

通用类用法:值:一个真的第一==第二是真的

generic class usage: values: a a true first == second is true

所以，我认为这表明'a'被自动装箱到Character.valueOf.

So, I think this demonstrates that 'a' is autoboxed to Character.valueOf.

我错过了什么吗?这是检查的正确方法吗?

Am I missing something? Is this the right way to check it?

谢谢.

Eliyahu

推荐答案

是的，自动装箱是使用 valueOf 到处进行的，以利用所有缓存.例如，使用 Character :

Yes, autoboxing is done with valueOf everywhere to take advantage of any caches. For example with Character:

public static Character valueOf(char c) {
    if (c <= 127) { // must cache
        return CharacterCache.cache[(int)c];
    }
    return new Character(c);
}

这是文档疏忽.

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