How to see if an object is an array without using reflection

Question

How can I see in Java if an Object is an array without using reflection  And how can I iterate through all items without using reflection   I use Google GWT so I am not allowed to use reflection     I would love to implement the following methods without using refelection   private boolean isArray final Object obj                private String toString final Object arrayObject                 BTW  neither do I want to use JavaScript such that I can use it in non-GWT environments

User · Answer

You can create a utility class to check if the class represents any Collection  Map or Array    public static boolean isCollection Class lt   gt  rawPropertyType            return Collection class isAssignableFrom rawPropertyType                     Map class isAssignableFrom rawPropertyType                     rawPropertyType isArray

User · Answer

There is no subtyping relationship between arrays of primitive type  or between an array of a primitive type and array of a reference type   See JLS 4 10 3   Therefore  the following is incorrect as a test to see if obj is an array of any kind      INCORRECT  public boolean isArray final Object obj        return obj instanceof Object        Specifically  it doesn t work if obj is 1-D array of primitives    It does work for primitive arrays with higher dimensions though  because all array types are subtypes of Object   But it is moot in this case       I use Google GWT so I am not allowed to use reflection      The best solution  to the isArray array part of the question  depends on what counts as  using reflection     In GWT  calling obj getClass   isArray   does not count as using reflection1  so that is the best solution    Otherwise  the best way of figuring out whether an object has an array type is to use a sequence of instanceof expressions     public boolean isArray final Object obj        return obj instanceof Object      obj instanceof boolean             obj instanceof byte      obj instanceof short             obj instanceof char      obj instanceof int             obj instanceof long      obj instanceof float             obj instanceof double       You could also try messing around with the name of the object s class as follows  but the call to obj getClass   is bordering on reflection   public boolean isArray final Object obj        return obj getClass   toString   charAt 0                 1 - More precisely  the Class isArray method is listed as supported by GWT in this page

User · Answer

One can access each element of an array separately using the following code   Object o      if   o getClass   isArray           for int i 0  i lt Array getLength o   i             System out println Array get o  i              Notice that it is unnecessary to know what kind of underlying array it is  as this will work for any array

User · Answer

You can use Class isArray    public static boolean isArray Object obj        return obj  null  amp  amp  obj getClass   isArray        This works for both object and primitive type arrays   For toString take a look at Arrays toString  You ll have to check the array type and call the appropriate toString method

User · Answer

You can use instanceof  JLS 15 20 2 Type Comparison Operator instanceof   RelationalExpression      RelationalExpression instanceof ReferenceType  At run time  the result of the instanceof operator is true if the value of the RelationalExpression is not null and the reference could be cast to the ReferenceType without raising a ClassCastException  Otherwise the result is false   That means you can do something like this  Object o   new int     1 2    System out println o instanceof int        prints  quot true quot           You d have to check if the object is an instanceof boolean    byte    short    char    int    long    float    double    or Object    if you want to detect all array types  Also  an int     is an instanceof Object    so depending on how you want to handle nested arrays  it can get complicated  For the toString  java util Arrays has a toString int    and other overloads you can use  It also has deepToString Object    for nested arrays  public String toString Object arr       if  arr instanceof int            return Arrays toString  int    arr        else          It s going to be very repetitive  but even java util Arrays is very repetitive   but that s the way it is in Java with arrays  See also  Managing highly repetitive code and documentation in Java Java Arrays equals   returns false for two dimensional arrays

User · Answer

Simply obj instanceof Object    tested on JShell

[java] How to see if an object is an array without using reflection?

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