Java class get primitive type

Get the name of a primitive type in Java

TYPE question Question: Is it possible to get the data type of an input variable (could be any primitive type, int, bool, float, double) returned as a string by using just one line of code? The get/set methods always use objects so you don’t need to know if the field is a primitive type (unless you try to set a primitive type to the null value.)

Get the name of a primitive type in Java

The getName() method is used to get the names of the entities such as primitive type, interface, class, array class, void etc. that represented by the class objects. These names are returned in the form of a string.

A program that gets the name of a primitive type using getName() method is given as follows —

Example

Output

Now let us understand the above program.

The getName() method is used to get the names of the primitive data types float, int and char. Then these names are stored in name1, name2 and name3 respectivel and displayed. A code snippet which demonstrates this is as follows −

String name1 = float.class.getName(); System.out.println(name1); String name2 = int.class.getName(); System.out.println(name2); String name3 = char.class.getName(); System.out.println(name3);

How to get primitive type from object in Java?, In this case you are talking about primitives, not classes. There is no need to find out what x is, because if you defined it as int x it can

Understanding Java Primitive Data Types

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Check type of primitive field

I’m trying to determine the type of a field on an object. I don’t know the type of the object when it is passed to me but I need to find fields which are long s. It is easy enough to distinguish the boxed Long s but the primitive long seems more difficult.

I can make sure that the objects passed to me only have Longs , not the primitives, but I’d rather not. So what I have is:

for (Field f : o.getClass().getDeclaredFields()) < Classclazz = f.getType(); if (clazz.equals(Long.class)) < // found one -- I don't get here for primitive longs >> 

A hacky way, which seems to work, is this:

for (Field f : o.getClass().getDeclaredFields()) < Classclazz = f.getType(); if (clazz.equals(Long.class) || clazz.getName().equals("long")) < // found one >> 

I’d really like a cleaner way to do this if there is one. If there is no better way then I think that requiring the objects I receive to only use Long (not long ) would be a better API.

You’re using the wrong constant to check for Long primitives — use Long.TYPE , each other primitive type can be found with a similarly named constant on the wrapper. eg: Byte.TYPE , Character.TYPE , etc.

o.getClass().getField("fieldName").getType().isPrimitive(); 

boolean.class byte.class char.class short.class int.class long.class float.class double.class void.class 

If you are using reflection, why do you care, why do this check at all. The get/set methods always use objects so you don’t need to know if the field is a primitive type (unless you try to set a primitive type to the null value.)

In fact, for the method get() you don’t need to know which type it is. You can do

// any number type is fine. Number n = field.get(object); long l = n.longValue(); 

If you are not sure if it is a Number type you can do

Object o = field.get(object); // will always be an Object or null. if (o instanceof Number) < Number n = (Number) o; long l = n.longValue(); 

• To detect fields with long type use long.class or Long.TYPE .
• To detect fields with Long type use Long.class .

for (Field f : o.getClass().getDeclaredFields()) < Classclazz = f.getType(); // to detect both Long and long types if (Long.class.equals(clazz) || long.class.equals(clazz)) < // found one >> 

Long.TYPE is static Constant member and is equivalent to long.class .

snippet code form Long Class

/** * The object that represents the primitive type . */ @SuppressWarnings("unchecked") public static final Class TYPE = (Class) long[].class.getComponentType(); 

Also check for answer for Difference between Integer.class and Integer.TYPE question

Checking the input for primitive data types in java, Of course it'll fail. Take a byte . In Java, it is represented as a signed 8bit value (2's complement notation). It means its range varies

Java - getting variable type for primitive data types

Is it possible to get the data type of an input variable (could be any primitive type, int, bool, float, double) returned as a string by using just one line of code? I know this can easily be done for a String type using getName and getShortName but I am unsure of how to use these methods to return the type of a primitive type. I also want to keep my code very short for doing this preferably using just one line.

I have searched around and cannot find anywhere this question has been answered in the way I require.

Returns the name of the entity (class, interface, array class, primitive type, or void) represented by this Class object, as a String. 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, Second Edition.

If this class object represents a primitive type or void, then the name returned is a String equal to the Java language keyword corresponding to the primitive type or void .

You can follow this link in the Java Doc that explain very well how to use this method.

How to determine the primitive type of a primitive variable?, You can't use isInstance for primitive types -- e.g. calling Integer.TYPE.isInstance(5) ( Integer.TYPE is equivalent to int.class ) will

Checking the input for primitive data types in java

I was given to code a program that would take input of a number and check, in which all primitive data types(byte, short, int, long) it will fit in. I wrote the following code but it is not passing all the test cases:

import java.util.*; import java.io.*; class Solution < public static void main(String []args) < Scanner sc = new Scanner(System.in); int t=sc.nextInt(); for(int i=0;i=-Byte.MAX_VALUE && x<=Byte.MAX_VALUE) System.out.println("* byte"); if(x>=-Short.MAX_VALUE && x<=Short.MAX_VALUE) System.out.println("* short"); if(x>=-Integer.MAX_VALUE && x<=Integer.MAX_VALUE) System.out.println("* int"); if(x>=-Long.MAX_VALUE && x <=Long.MAX_VALUE) System.out.println("* long"); >catch(Exception e) < System.out.println(sc.next()+" can't be fitted anywhere."); >> > > 

Of course it'll fail. Take a byte . In Java, it is represented as a signed 8bit value (2's complement notation). It means its range varies from -128 to +127. You logic says that it'll be a byte if it lies b/w (inclusive of both sides), -127 to +127. It'll fail for -128.

Replace -Byte.MAX_VALUE with Byte.MIN_VALUE and it'll work.

You should be using if . else logic here, to prevent a given input from matching more than one case:

long x = sc.nextLong(); System.out.println(x+" can be fitted in:"); if (x >= Byte.MIN_VALUE && x else if (x >= Short.MIN_VALUE && x else if (x >= Integer.MIN_VALUE && x else if (x >= Long.MIN_VALUE && x else

I hope if you give a value which can't be taken by a long variable, the value will wrap around between long.max_value & long.min_value. What i can suggest is, get the input as a string from the user and construct BigDecimal and compare the range values of the primitives with the BigDecimal Values using some builtin methods.

Why Java Collections Cannot Directly Store Primitives Types?, Primitive types are the most basic data types available within the Java language. Such types serve only one purpose — containing pure,

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Retrieving Class Objects

The entry point for all reflection operations is java.lang.Class . With the exception of java.lang.reflect.ReflectPermission , none of the classes in java.lang.reflect have public constructors. To get to these classes, it is necessary to invoke appropriate methods on Class . There are several ways to get a Class depending on whether the code has access to an object, the name of class, a type, or an existing Class .

Object.getClass()

If an instance of an object is available, then the simplest way to get its Class is to invoke Object.getClass() . Of course, this only works for reference types which all inherit from Object . Some examples follow.

Class c = System.console().getClass();

There is a unique console associated with the virtual machine which is returned by the static method System.console() . The value returned by getClass() is the Class corresponding to java.io.Console .

enum E < A, B >Class c = A.getClass();

A is an instance of the enum E ; thus getClass() returns the Class corresponding to the enumeration type E .

byte[] bytes = new byte[1024]; Class c = bytes.getClass();

Since arrays are Objects , it is also possible to invoke getClass() on an instance of an array. The returned Class corresponds to an array with component type byte .

import java.util.HashSet; import java.util.Set; Set s = new HashSet(); Class c = s.getClass();

In this case, java.util.Set is an interface to an object of type java.util.HashSet . The value returned by getClass() is the class corresponding to java.util.HashSet .

The .class Syntax

If the type is available but there is no instance then it is possible to obtain a Class by appending ".class" to the name of the type. This is also the easiest way to obtain the Class for a primitive type.

boolean b; Class c = b.getClass(); // compile-time error Class c = boolean.class; // correct

Note that the statement boolean.getClass() would produce a compile-time error because a boolean is a primitive type and cannot be dereferenced. The .class syntax returns the Class corresponding to the type boolean .

Class c = java.io.PrintStream.class;

The variable c will be the Class corresponding to the type java.io.PrintStream .

The .class syntax may be used to retrieve a Class corresponding to a multi-dimensional array of a given type.

Class.forName()

If the fully-qualified name of a class is available, it is possible to get the corresponding Class using the static method Class.forName() . This cannot be used for primitive types. The syntax for names of array classes is described by Class.getName() . This syntax is applicable to references and primitive types.

Class c = Class.forName("com.duke.MyLocaleServiceProvider");

This statement will create a class from the given fully-qualified name.

Class cDoubleArray = Class.forName("[D"); Class cStringArray = Class.forName("[[Ljava.lang.String;");

The variable cDoubleArray will contain the Class corresponding to an array of primitive type double (that is, the same as double[].class ). The cStringArray variable will contain the Class corresponding to a two-dimensional array of String (that is, identical to String[][].class ).

TYPE Field for Primitive Type Wrappers

The .class syntax is a more convenient and the preferred way to obtain the Class for a primitive type; however there is another way to acquire the Class . Each of the primitive types and void has a wrapper class in java.lang that is used for boxing of primitive types to reference types. Each wrapper class contains a field named TYPE which is equal to the Class for the primitive type being wrapped.

There is a class java.lang.Double which is used to wrap the primitive type double whenever an Object is required. The value of Double.TYPE is identical to that of double.class .

Void.TYPE is identical to void.class .

Methods that Return Classes

There are several Reflection APIs which return classes but these may only be accessed if a Class has already been obtained either directly or indirectly.

Class.getSuperclass() Returns the super class for the given class.

Class c = javax.swing.JButton.class.getSuperclass();

The super class of javax.swing.JButton is javax.swing.AbstractButton . Class.getClasses() Returns all the public classes, interfaces, and enums that are members of the class including inherited members.

Class[] c = Character.class.getClasses();

Character contains two member classes Character.Subset and Character.UnicodeBlock . Class.getDeclaredClasses() Returns all of the classes interfaces, and enums that are explicitly declared in this class.

Class[] c = Character.class.getDeclaredClasses();

import java.lang.reflect.Field; Field f = System.class.getField("out"); Class c = f.getDeclaringClass();

public class MyClass < static Object o = new Object() < public void m() <>>; static Class = o.getClass().getEnclosingClass(); >

The declaring class of the anonymous class defined by o is null . Class.getEnclosingClass() Returns the immediately enclosing class of the class.

Class c = Thread.State.class().getEnclosingClass();

public class MyClass < static Object o = new Object() < public void m() <>>; static Class = o.getClass().getEnclosingClass(); >

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