null 是个什么东西？？ 是常量？？ 关键字？？

[wren4255]

谢谢！！

把null看成个对象，System.out.printf(null);不行么？？

[nihuajie05]

[Quote=引用 4 楼 bao110908 的回复:]
An identifier cannot have the same spelling (Unicode character sequence) as a keyword, boolean literal, or the null literal.
(Excerpt from: http://java.sun.com/docs/books/jls/third_edition/html/lexical.html#3.8)

The null type has one value, the null reference, represented by the literal null, which is formed from ASCII characters. A null literal is always of the null type.
(Excerpt from:…
[/Quote]
西西

[haoxiongok]

[Quote=引用 4 楼 bao110908 的回复:]
An identifier cannot have the same spelling (Unicode character sequence) as a keyword, boolean literal, or the null literal.
(Excerpt from: http://java.sun.com/docs/books/jls/third_edition/html/lexical.html#3.8)

The null type has one value, the null reference, represented by the literal null, which is formed from ASCII characters. A null literal is always of the null type.
(Excerpt from:…
[/Quote]

牛牛牛，果子厉害

[chensjmail]

其实你就可以把它看成是一个特殊的对象，这个对象的引用没有指向任务的内存位置

[不懂编程]

厉害，学习

[aa321207]

顶起4楼
好样的

[classnameextendsjava]

它没toString()方法 所以直接print不起来

[suifeng0117]

又长了一点儿知识!支持高人讲解!

[胡矣]

aha

[healer_kx]

null是关键字是肯定的了。其实我觉得你可以把null看成是一个带有字符串色彩的常量。

[贝壳鱼]

NULL 不是对象，只是个关键字。表示未初始化的，无值的。

[dracularking]

null就是无 在java中它是关键字 某种程度上可以理解为对象 因为可以赋予object reference 表示引用为空
但不是对象 不符合对象特征
这样使用null会输出NullPointerException

[火龙果被占用了]

An identifier cannot have the same spelling (Unicode character sequence) as a keyword, boolean literal, or the null literal.
(Excerpt from: http://java.sun.com/docs/books/jls/third_edition/html/lexical.html#3.8)

The null type has one value, the null reference, represented by the literal null, which is formed from ASCII characters. A null literal is always of the null type.
(Excerpt from: http://java.sun.com/docs/books/jls/third_edition/html/lexical.html#230717)

首先，null 不是关键词；
其次，null 有一个值，即空引用

Java 中方法的传值方式基本上是按引用来传递，代码中传入 null 时，其引用的对象为空，所以会出空指针错误。

[dracularking]

多谢火龙果 长见识了 有空要细读这些文档
null非关键字 是和Identifiers Keywords, boolean literals等并列的null literal

[rabbit_zizhu]

恩.java中null,false,true这些是常量,不是关键字.但也不能用它们创建标识符
对编译器来说,null是一个值.null值指引用变量没有引用堆上的任何对象.