CharSequence接口在方法定义中的应用

String 是java中的字符串，它继承于CharSequence。
StringBuilder 和 StringBuffer都是可变的字符序列。它们都继承于AbstractStringBuilder，实现了CharSequence接口。

但是，StringBuilder是非线程安全的，而StringBuffer是线程安全的。
CharSequence接口在方法定义中的应用

附录：spring StringUtils部分源码

/**

* Check that the given CharSequence is neither {@code null} nor of length 0.

* Note: Will return {@code true} for a CharSequence that purely consists of whitespace.

* <p><pre class="code">

* StringUtils.hasLength(null) = false

* StringUtils.hasLength("") = false

* StringUtils.hasLength(" ") = true

* StringUtils.hasLength("Hello") = true

* </pre>

* @param str the CharSequence to check (may be {@code null})

* @return {@code true} if the CharSequence is not null and has length

* @see #hasText(String)

public static boolean hasLength(CharSequence str) {

return (str != null && str.length() > 0);

}