Get variable name java

How can I print the name of a variable in Java?

You can’t print just the name of a variable. However, I can show you a way to print the name of a class variable.

(AKA if you want to print the name of a variable, make it a class variable)

explanation

package Print; public class ClassVariable < void start() < >public static void main(String[] args) < new ClassVariable().start(); >>

package Print; public class ClassVariable < public String testVar; void start() < >public static void main(String[] args) < new ClassVariable().start(); >>

package Print; public class ClassVariable < public String testVar; void start() < ClassVariable newObject = new ClassVariable(); >public static void main(String[] args) < new ClassVariable().start(); >>

package Print; public class ClassVariable < public String testVar; void start() < ClassVariable newObject = new ClassVariable(); Class newClassObject = newObject.getClass(); >public static void main(String[] args) < new ClassVariable().start(); >>

package Print; import java.lang.reflect.Field; public class ClassVariable < public String testVar; void start() < ClassVariable newObject = new ClassVariable(); Class newClassObject = newObject.getClass(); Field variable = newClassObject.getField("testVar");a >public static void main(String[] args) < new ClassVariable().start(); >>

package Print; import java.lang.reflect.Field; public class ClassVariable < public String testVar; void start() throws NoSuchFieldException, SecurityException < ClassVariable newObject = new ClassVariable(); Class newClassObject = newObject.getClass(); Field variable = newClassObject.getField("testVar"); >public static void main(String[] args) throws NoSuchFieldException, SecurityException < new ClassVariable().start(); >>

package Print; import java.lang.reflect.Field; public class ClassVariable < public String testVar; void start() throws NoSuchFieldException, SecurityException < ClassVariable newObject = new ClassVariable(); Class newClassObject = newObject.getClass(); Field variable = newClassObject.getField("testVar"); System.out.println("The name of the variable is: " + variable.getName()); >public static void main(String[] args) throws NoSuchFieldException, SecurityException < new ClassVariable().start(); >>

YOU HAVE PRINTED THE NAME OF A VARIABLE!

Источник

Is possible to get variable name in java?

posted 12 years ago

Hi,
I have two class. I want to get first class variable name. Not value.

Is possible?
Help me.
Thanks in advance.

Wake up! Don’t let your smile be snatched away by anybody!
Regards, Eswar

Sheriff

posted 12 years ago

Via reflection : Class#getFields() will return an array of fields. You can get their name via Field#getName()

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All roads lead to JavaRanch

posted 12 years ago

Subhash Kumar
Attitude is everything

Источник

How to get variable name in java class example| getDeclaredFields reflection

In this example, How to get variable names of a class using reflection.

Reflection package API in java provides to analyze and update behavior of java classes at runtime.

class or interface in java contains variables declared with different types and modifiers — public, final, private, default, protected, and static.

print public variable names of a java class using reflection API

getFields() method of an java.lang.Class gives list of all public aviable variable names of an interface or class in java.

here is an example of using the getFields method

import java.lang.reflect.Field; public class Main private Integer privateVariable = 1; public Integer value = 1; public String str = «helloworld»; public static String staticValue = «THIS IS STATIC»; public static final String finalValue = «THIS IS STATIC»; public static void main(String[] args) Main main= new Main(); Class class = main.getClass(); Field[] fields = class.getFields(); for(Field f: fields) System.out.println(f.getName()); > > >

value str staticValue finalValue

As you see, only public variable names are retrieved using the getFields() method, and private variables are not displayed.

How to retrieve private variable names of a class? getDeclaredFields() method of an class returns public ,protected, default and private variable of an class or interface.

Here is an example to retrieve all fields of a java class

import java.lang.reflect.Field; public class Main  private Integer privateVariable = 1; public Integer value = 1; public String str = "helloworld"; public static String staticValue = "THIS IS STATIC"; public static final String finalValue = "THIS IS STATIC"; public static void main(String[] args)  Main main= new Main(); Class myclass = main.getClass(); Field[] fields = myclass.getDeclaredFields(); for(Field f: fields) System.out.println(f.getName()); > > >

privateVariable value str staticValue finalValue

Источник

Java Reflection: How to get the name of a variable?

As of Java 8, some local variable name information is available through reflection. See the «Update» section below.

Complete information is often stored in class files. One compile-time optimization is to remove it, saving space (and providing some obsfuscation). However, when it is is present, each method has a local variable table attribute that lists the type and name of local variables, and the range of instructions where they are in scope.

Perhaps a byte-code engineering library like ASM would allow you to inspect this information at runtime. The only reasonable place I can think of for needing this information is in a development tool, and so byte-code engineering is likely to be useful for other purposes too.

Update: Limited support for this was added to Java 8. Parameter (a special class of local variable) names are now available via reflection. Among other purposes, this can help to replace @ParameterName annotations used by dependency injection containers.

Solution 2

It is not possible at all. Variable names aren’t communicated within Java (and might also be removed due to compiler optimizations).

EDIT (related to comments):

If you step back from the idea of having to use it as function parameters, here’s an alternative (which I wouldn’t use — see below):

public void printFieldNames(Object obj, Foo. foos) < ListfooList = Arrays.asList(foos); for(Field field : obj.getClass().getFields()) < if(fooList.contains(field.get()) < System.out.println(field.getName()); >> > 

There will be issues if a == b, a == r, or b == r or there are other fields which have the same references.

EDIT now unnecessary since question got clarified

Solution 3

(Edit: two previous answers removed, one for answering the question as it stood before edits and one for being, if not absolutely wrong, at least close to it.)

If you compile with debug information on ( javac -g ), the names of local variables are kept in the .class file. For example, take this simple class:

After compiling with javac -g:vars TestLocalVarNames.java , the names of local variables are now in the .class file. javap ‘s -l flag («Print line number and local variable tables») can show them.

javap -l -c TestLocalVarNames shows:

class TestLocalVarNames extends java.lang.Object< TestLocalVarNames(); Code: 0: aload_0 1: invokespecial #1; //Method java/lang/Object."":()V 4: return LocalVariableTable: Start Length Slot Name Signature 0 5 0 this LTestLocalVarNames; public java.lang.String aMethod(int); Code: 0: ldc #2; //String a string 2: astore_2 3: new #3; //class java/lang/StringBuilder 6: dup 7: invokespecial #4; //Method java/lang/StringBuilder."":()V 10: astore_3 11: aload_3 12: aload_2 13: invokevirtual #5; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder; 16: iload_1 17: invokevirtual #6; //Method java/lang/StringBuilder.append:(I)Ljava/lang/StringBuilder; 20: invokevirtual #7; //Method java/lang/StringBuilder.toString:()Ljava/lang/String; 23: areturn LocalVariableTable: Start Length Slot Name Signature 0 24 0 this LTestLocalVarNames; 0 24 1 arg I 3 21 2 local1 Ljava/lang/String; 11 13 3 local2 Ljava/lang/StringBuilder; > 

The VM spec explains what we’re seeing here:

The LocalVariableTable attribute is an optional variable-length attribute of a Code (§4.7.3) attribute. It may be used by debuggers to determine the value of a given local variable during the execution of a method.

The LocalVariableTable stores the names and types of the variables in each slot, so it is possible to match them up with the bytecode. This is how debuggers can do «Evaluate expression».

As erickson said, though, there’s no way to access this table through normal reflection. If you’re still determined to do this, I believe the Java Platform Debugger Architecture (JPDA) will help (but I’ve never used it myself).

Solution 4

import java.lang.reflect.Field; public class test < public int i = 5; public Integer test = 5; public String omghi = "der"; public static String testStatic = "THIS IS STATIC"; public static void main(String[] args) throws IllegalArgumentException, IllegalAccessException < test t = new test(); for(Field f : t.getClass().getFields()) < System.out.println(f.getGenericType() +" "+f.getName() + " btn btn-outline-primary" role="button" data-toggle="collapse" aria-expanded="false" aria-controls="moreSolutions" href="#moreSolutions">View more solutions 

Foo b = new Foo(); Foo a = new Foo(); Foo r = new Foo(); 

import java.lang.reflect.Field; import java.lang.reflect.ParameterizedType; public class ClassFieldsReflection < public static void main(String[] args) < ClassFieldsReflection objClassFieldsReflection = new ClassFieldsReflection(); objClassFieldsReflection.AccessFieldsUsingReflection(new Actor()); >/** * Access fields of Object using Reflection. * @param obj */ private void AccessFieldsUsingReflection(Object obj)< /* Get array of fields declared in Class */ Field[] fields = obj.getClass().getDeclaredFields(); /* Loop through all fields */ for(int i = 0; i < fields.length ; i++)< /* Get field name */ String fieldName = fields[i].getName(); /* Get generic/base type of field (int, short, long, String, etc. ) */ Object fieldType = fields[i].getGenericType(); System.out.println("Field(variable) name: " + fieldName); System.out.println("Generic Type: " + fieldType); /* Set, List and Map are ParameterizedType */ if(fieldType instanceof ParameterizedType)< /** * This will give you Actual Type of Set, List and Map. * Example: * List -> String is ActualType * Set -> Integer is ActualType * Map -> String, Long is ActualType */ System.out.println("Actual Type:"); for(Object objActualType : ((ParameterizedType) fieldType).getActualTypeArguments()) < System.out.println("-- "+objActualType); >> System.out.println("+++++++++++++++++++++++++++++++"); > > >

Field(variable) name: id Generic Type: long +++++++++++++++++++++++++++++++ Field(variable) name: Name Generic Type: class java.lang.String +++++++++++++++++++++++++++++++ Field(variable) name: Films Generic Type: java.util.Set Actual Type: -- class javaQuery.beans.Film +++++++++++++++++++++++++++++++ Field(variable) name: LanguageSpeaks Generic Type: java.util.List Actual Type: -- class javaQuery.beans.Language +++++++++++++++++++++++++++++++ Field(variable) name: dummyMap Generic Type: java.util.Map Actual Type: -- class java.lang.String -- class java.lang.Long +++++++++++++++++++++++++++++++