将Char作为参数传递给其重载的构造函数时，StringBuffer的行为如何？ [英] How StringBuffer behaves When Passing Char as argument to its Overloaded Constructor?

问题描述

    StringBuffer sb = new StringBuffer('A');
    System.out.println("sb = " + sb.toString());
    sb.append("Hello");
    System.out.println("sb = " + sb.toString());

输出：

sb =

sb =

sb =你好

但如果我通过一个字符串而不是字符，它附加到Hello。
为什么这个奇怪的行为有char？

But if i pass a String instead of character, it appends to Hello . Why is this strange behavior with char ?

推荐答案

没有构造函数接受炭。您最终获得了 <$ c由于Java自动将 char 转换为 int int 构造函数 c>，从而指定初始容量。

There is no constructor which accepts a char. You end up with the int constructor due to Java automatically converting your char to an int, thus specifying the initial capacity.

/**
 * Constructs a string buffer with no characters in it and
 * the specified initial capacity.
 *
 * @param      capacity  the initial capacity.
 * @exception  NegativeArraySizeException  if the <code>capacity</code>
 *               argument is less than <code>0</code>.
 */
public StringBuffer(int capacity) {
    super(capacity);
}

Cf。这个最小的例子：

Cf. this minimal example:

public class StringBufferTest {
    public static void main(String[] args) {
        StringBuffer buf = new StringBuffer('a');
        System.out.println(buf.capacity());
        System.out.println((int) 'a');
        StringBuffer buf2 = new StringBuffer('b');
        System.out.println(buf2.capacity());
        System.out.println((int) 'b');
    }
}

输出：

97
97
98
98

然而

StringBuffer buf3 = new StringBuffer("a");
System.out.println(buf3.capacity());

结果初始容量 17 。

您可能已将<$ h $ => http://docs.oracle.com/javase与 char 混淆/7/docs/api/java/lang/CharSequence.html\"rel =nofollow> CharSequence （确实有一个构造函数），但是这是完全不同的两件事。

You might have confused char with CharSequence (for which there is indeed a constructor), but these are two completely different things.

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