for "%b" : 如果参数 arg 为 null，则结果为 "false".如果 arg 是布尔值或布尔值，则结果是 String.valueOf() 返回的字符串.否则，结果为真".

for "%b" : If the argument arg is null, then the result is "false". If arg is a boolean or Boolean, then the result is the string returned by String.valueOf(). Otherwise, the result is "true".

参考