What is this Ljava lang Object

Question

I get this when I call toString on an object I received from a function call  I know the type of the object is encoded in this string  but I don t know how to read it   What is this type of encoding called

User · Answer

If you are here because of the Liquibase error saying:

Caused By: Precondition Error
...
Can't detect type of array [Ljava.lang.Short

and you are using

not {
  indexExists()
}

precondition multiple times, then you are facing an old bug: https://liquibase.jira.com/browse/CORE-1342

We can try to execute an above check using bare sqlCheck(Postgres):

SELECT COUNT(i.relname)
FROM
    pg_class t,
    pg_class i,
    pg_index ix
WHERE
    t.oid = ix.indrelid
    and i.oid = ix.indexrelid
    and t.relkind = 'r'
    and t.relname = 'tableName'
    and i.relname = 'indexName';

where tableName - is an index table name and indexName - is an index name

User · Answer

Ljava lang Object  is the name for Object   class  the java lang Class representing the class of array of Object   The naming scheme is documented in Class getName        If this class object represents a reference type that is not an array type then the binary name of the class is returned  as specified by the Java Language Specification    13 1        If this class object represents a primitive type or void  then the name returned is the Java language keyword corresponding to the primitive type or void        If this class object represents a class of arrays  then the internal form of the name consists of the name of the element type preceded by one or more     characters representing the depth of the array nesting    The encoding of element type names is as follows   Element Type        Encoding boolean             Z byte                B char                C double              D float               F int                 I long                J short               S  class or interface  Lclassname     Yours is the last on that list   Here are some examples      xxxxx varies System out println new int 0  0  7          I xxxxx System out println new String 4  2         Ljava lang String  xxxxx System out println new boolean 256        Z xxxxx   The reason why the toString   method on arrays returns String in this format is because arrays do not  Override the method inherited from Object  which is specified as follows      The toString method for class Object returns a string consisting of the name of the class of which the object is an instance  the at-sign character      and the unsigned hexadecimal representation of the hash code of the object  In other words  this method returns a string equal to the value of   getClass   getName           Integer toHexString hashCode       Note  you can not rely on the toString   of any arbitrary object to follow the above specification  since they can  and usually do   Override it to return something else  The more reliable way of inspecting the type of an arbitrary object is to invoke getClass   on it  a final method inherited from Object  and then reflecting on the returned Class object  Ideally  though  the API should ve been designed such that reflection is not necessary  see Effective Java 2nd Edition  Item 53  Prefer interfaces to reflection      On a more  useful  toString for arrays  java util Arrays provides toString overloads for primitive arrays and Object    There is also deepToString that you may want to use for nested arrays   Here are some examples   int   nums     1  2  3     System out println nums       I xxxxx  System out println Arrays toString nums        1  2  3   int     table               1               2  3               4  5  6         System out println Arrays toString table         I xxxxx   I yyyyy   I zzzzz   System out println Arrays deepToString table         1    2  3    4  5  6     There are also Arrays equals and Arrays deepEquals that perform array equality comparison by their elements  among many other array-related utility methods   Related questions   Java Arrays equals   returns false for two dimensional arrays  -- in-depth coverage

[java] What is this: [Ljava.lang.Object;?

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