问题
How can I cast an Object to an int in java?
回答1:
If you're sure that this object is an Integer :
int i = (Integer) object;
Or, starting from Java 7, you can equivalently write:
int i = (int) object;
Beware, it can throw a ClassCastException if your object isn't an Integer and a NullPointerException if your object is null.
This way you assume that your Object is an Integer (the wrapped int) and you unbox it into an int.
int is a primitive so it can't be stored as an Object, the only way is to have an int considered/boxed as an Integer then stored as an Object.
If your object is a String, then you can use the Integer.valueOf() method to convert it into a simple int :
int i = Integer.valueOf((String) object);
It can throw a NumberFormatException if your object isn't really a String with an integer as content.
Resources :
- Oracle.com - Autoboxing
- Oracle.com - Primitive Data types
On the same topic :
- Java: What's the difference between autoboxing and casting?
- Autoboxing: So I can write: Integer i = 0; instead of: Integer i = new Integer(0);
- Convert Object into primitive int
回答2:
Assuming the object is an Integer object, then you can do this:
int i = ((Integer) obj).intValue();
If the object isn't an Integer object, then you have to detect the type and convert it based on its type.
回答3:
@Deprecated
public static int toInt(Object obj)
{
if (obj instanceof String)
{
return Integer.parseInt((String) obj);
} else if (obj instanceof Number)
{
return ((Number) obj).intValue();
} else
{
String toString = obj.toString();
if (toString.matches("-?\d+"))
{
return Integer.parseInt(toString);
}
throw new IllegalArgumentException("This Object doesn't represent an int");
}
}
As you can see, this isn't a very efficient way of doing it. You simply have to be sure of what kind of object you have. Then convert it to an int the right way.
回答4:
Scenario 1: simple case
If it's guaranteed that your object is an Integer, this is the simple way:
int x = (Integer)yourObject;
Scenario 2: any numerical object
In Java Integer, Long, BigInteger etc. all implement the Number interface which has a method named intValue. Any other custom types with a numerical aspect should also implement Number (for example: Age implements Number). So you can:
int x = ((Number)yourObject).intValue();
Scenario 3: parse numerical text
When you accept user input from command line (or text field etc.) you get it as a String. In this case you can use Integer.parseInt(String string):
String input = someBuffer.readLine();
int x = Integer.parseInt(input);
If you get input as Object, you can use (String)input, or, if it can have an other textual type, input.toString():
int x = Integer.parseInt(input.toString());
Scenario 4: identity hash
In Java there are no pointers. However Object has a pointer-like default implementation for hashCode(), which is directly available via System.identityHashCode(Object o). So you can:
int x = System.identityHashCode(yourObject);
Note that this is not a real pointer value. Objects' memory address can be changed by the JVM while their identity hashes are keeping. Also, two living objects can have the same identity hash.
You can also use object.hashCode(), but it can be type specific.
Scenario 5: unique index
In same cases you need a unique index for each object, like to auto incremented ID values in a database table (and unlike to identity hash which is not unique). A simple sample implementation for this:
class ObjectIndexer {
private int index = 0;
private Map<Object, Integer> map = new WeakHashMap<>();
public int indexFor(Object object) {
if (map.containsKey(object)) {
return map.get(object);
} else {
index++;
map.put(object, index);
return index;
}
}
}
Usage:
ObjectIndexer indexer = new ObjectIndexer();
int x = indexer.indexFor(yourObject); // 1
int y = indexer.indexFor(new Object()); // 2
int z = indexer.indexFor(yourObject); // 1
Scenario 6: enum member
In Java enum members aren't integers but full featured objects (unlike C/C++, for example). Probably there is never a need to convert an enum object to int, however Java automatically associates an index number to each enum member. This index can be accessed via Enum.ordinal(), for example:
enum Foo { BAR, BAZ, QUX }
// ...
Object baz = Foo.BAZ;
int index = ((Enum)baz).ordinal(); // 1
回答5:
You have to cast it to an Integer (int's wrapper class). You can then use Integer's intValue() method to obtain the inner int.
回答6:
Answer:
int i = ( Integer ) yourObject;
If, your object is an integer already, it will run smoothly. ie:
Object yourObject = 1;
// cast here
or
Object yourObject = new Integer(1);
// cast here
etc.
If your object is anything else, you would need to convert it ( if possible ) to an int first:
String s = "1";
Object yourObject = Integer.parseInt(s);
// cast here
Or
String s = "1";
Object yourObject = Integer.valueOf( s );
// cast here
回答7:
I use a one-liner when processing data from GSON:
int i = object != null ? Double.valueOf(object.toString()).intValue() : 0;
回答8:
If the Object was originally been instantiated as an Integer, then you can downcast it to an int using the cast operator (Subtype).
Object object = new Integer(10);
int i = (Integer) object;
Note that this only works when you're using at least Java 1.5 with autoboxing feature, otherwise you have to declare i as Integer instead and then call intValue() on it.
But if it initially wasn't created as an Integer at all, then you can't downcast like that. It would result in a ClassCastException with the original classname in the message. If the object's toString() representation as obtained by String#valueOf() denotes a syntactically valid integer number (e.g. digits only, if necessary with a minus sign in front), then you can use Integer#valueOf() or new Integer() for this.
Object object = "10";
int i = Integer.valueOf(String.valueOf(object));
See also:
- Inheritance and casting tutorial
回答9:
int i = (Integer) object; //Type is Integer.
int i = Integer.parseInt((String)object); //Type is String.
回答10:
Can't be done. An int is not an object, it's a primitive type. You can cast it to Integer, then get the int.
Integer i = (Integer) o; // throws ClassCastException if o.getClass() != Integer.class
int num = i; //Java 1.5 or higher
回答11:
You can't. An int is not an Object.
Integer is an Object though, but I doubt that's what you mean.
回答12:
If you mean cast a String to int, use Integer.valueOf("123").
You can't cast most other Objects to int though, because they wont have an int value. E.g. an XmlDocument has no int value.
回答13:
I guess you're wondering why C or C++ lets you manipulate an object pointer like a number, but you can't manipulate an object reference in Java the same way.
Object references in Java aren't like pointers in C or C++... Pointers basically are integers and you can manipulate them like any other int. References are intentionally a more concrete abstraction and cannot be manipulated the way pointers can.
回答14:
int[] getAdminIDList(String tableName, String attributeName, int value) throws SQLException {
ArrayList list = null;
Statement statement = conn.createStatement();
ResultSet result = statement.executeQuery("SELECT admin_id FROM " + tableName + " WHERE " + attributeName + "='" + value + "'");
while (result.next()) {
list.add(result.getInt(1));
}
statement.close();
int id[] = new int[list.size()];
for (int i = 0; i < id.length; i++) {
try {
id[i] = ((Integer) list.get(i)).intValue();
} catch(NullPointerException ne) {
} catch(ClassCastException ch) {}
}
return id;
}
// enter code here
This code shows why ArrayList is important and why we use it. Simply casting int from Object. May be its helpful.
回答15:
For Example Object variable; hastaId
Object hastaId = session.getAttribute("hastaID");
For Example Cast an Object to an int,hastaID
int hastaID=Integer.parseInt(String.valueOf(hastaId));
回答16:
Refer This code:
public class sample
{
public static void main(String[] args)
{
Object obj=new Object();
int a=10,b=0;
obj=a;
b=(int)obj;
System.out.println("Object="+obj+"\nB="+b);
}
}
回答17:
so divide1=me.getValue()/2;
int divide1 = (Integer) me.getValue()/2;
回答18:
Finally, the best implementation for your specification was found.
public int tellMyNumber(Object any) {
return 42;
}
回答19:
first check with instanceof keyword . if true then cast it.
来源：https://stackoverflow.com/questions/3661413/how-to-cast-an-object-to-an-int