How can I know if Object is String type object?

Question

I have to know if Object is String or any other class type, how can I do it? Currently I do it like below, but its not very good coding.

try {
    String myString = (String) object;
    // do stuff here
} catch(Exception e) {
    // it wasn't string, so just continue
}

Answer 1

 object instanceof Type

is true if the object is a Type or a subclass of Type

 object.getClass().equals(Type.class) 

is true only if the object is a Type

Answer 2

Use the instanceof syntax.

Like so:

Object foo = "";

if( foo instanceof String ) {
  // do something String related to foo
}

Answer 3

Guard your cast with instanceof

String myString;
if (object instanceof String) {
  myString = (String) object;
}

Answer 4

使用instanceof或方法Class.isAssignableFrom(Class<?> cls) 。

Answer 5

javamonkey79 is right. But don't forget what you might want to do (eg try something else or notify someone) if object is not an instance of String.

String myString;
if (object instanceof String) {
  myString = (String) object;
} else {
  // do something else     
}

BTW: If you use ClassCastException instead of Exception in your code above, you can be sure that you will catch the exception caused by casting object to String. And not any other exceptions caused by other code (eg NullPointerExceptions).

Answer 6

Its possible you don't need to know depending on what you are doing with it.

String myString = object.toString();

or if object can be null

String myString = String.valueOf(object);

Answer 7

From JDK 14+ which includes JEP 305 we can do Pattern Matching for instanceof

Patterns basically test that a value has a certain type, and can extract information from the value when it has the matching type.

Before Java 14

if (obj instanceof String) {
    String str = (String) obj; // need to declare and cast again the object
    .. str.contains(..) ..
}else{
     str = ....
}

Java 14 enhancements

if (!(obj instanceof String str)) {
    .. str.contains(..) .. // no need to declare str object again with casting
} else {
    .. str....
}

We can also combine the type check and other conditions together

if (obj instanceof String str && str.length() > 4) {.. str.contains(..) ..}

The use of pattern matching in instanceof should reduce the overall number of explicit casts in Java programs.

PS : instanceOf will only match when the object is not null, then only it can be assigned to str .

Answer 8

你能不能用 typeof(object) 来比较