java - 检查字符串是否不为空且不为空(Check whether a string is not null and not empty)

Question

How can I check whether a string is not null and not empty?

(如何检查字符串是否不为null也不为空？)

public void doStuff(String str)
{
    if (str != null && str != "**here I want to check the 'str' is empty or not**")
    {
        /* handle empty string */
    }
    /* ... */
}

  ask by translate from so

Answer 1

What about isEmpty() ?

(那isEmpty（）呢？)

if(str != null && !str.isEmpty())

Be sure to use the parts of && in this order, because java will not proceed to evaluate the second part if the first part of && fails, thus ensuring you will not get a null pointer exception from str.isEmpty() if str is null.

(确保按此顺序使用&&的部分，因为如果&&的第一部分失败，java将不会继续评估第二部分，因此，如果str为null，则确保不会从str.isEmpty()获得null指针异常。 。)

Beware, it's only available since Java SE 1.6.

(请注意，仅从Java SE 1.6起可用。)

You have to check str.length() == 0 on previous versions.

(您必须在以前的版本中检查str.length() == 0 。)

---

To ignore whitespace as well:

(也要忽略空格：)

if(str != null && !str.trim().isEmpty())

(since Java 11 str.trim().isEmpty() can be reduced to str.isBlank() which will also test for other Unicode white spaces)

(（因为Java 11 str.trim().isEmpty()可以简化为str.isBlank() ，这也将测试其他Unicode空格）)

Wrapped in a handy function:

(包裹在一个方便的功能中：)

public static boolean empty( final String s ) {
  // Null-safe, short-circuit evaluation.
  return s == null || s.trim().isEmpty();
}

Becomes:

(成为：)

if( !empty( str ) )