这个问题在这里已有答案:
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,我想确保我没错。我将非常感谢您的反馈。
我在https://docs.oracle.com/javase/tutorial/java/generics/restrictions.html看到了以下解释
配对<整数,字符> p =新配对<>(8,'a');
请注意,Java编译器将8自动装箱到Integer.valueOf(8),将'a'自动装箱到角色('a'):
配对<整数,字符> p =新配对<>(Integer.valueOf(8),新字符('a'));
我认为这是一个错误,'a'实际上是自动装入Character.valueOf('a')。
我编写了以下程序来检查它。因为我认为也许泛型有特殊拳击,我尝试了泛型方法,常规方法和泛型类:
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("=============");
}
}
输出是:
泛型方法用法:值:a a true first == second为true
常规方法用法:值:a a true first == second为true
泛型类用法:值:a a true first == second为true
所以,我认为这表明'a'被自动装箱到Character.valueOf。
我错过了什么吗?这是检查它的正确方法吗?
谢谢。
埃利亚胡
是的,自动装箱是用valueOf
到处完成的,以利用任何缓存。例如,使用Character
:
public static Character valueOf(char c) {
if (c <= 127) { // must cache
return CharacterCache.cache[(int)c];
}
return new Character(c);
}
这是一个文件疏忽。