January 22, 2021
java return two values of different types
I've just written this in response to comments, for illustration purposes only. In C, you would do it by passing pointers to placeholders for the results as arguments: Keep it simple and create a class for multiple result situation. I agree however with some other answers that if you need to return two or more objects from a method, it would be better to encapsulate them in a class. I want to return two objects from a Java method and was wondering what could be a good way of doing so? The finally block will always be executed except in the following example: In this case, the JVM will stop, without executing the finally block. And it is effective as it can even return values of Multiple Types e.g. return is a reserved keyword in Java i.e, we can’t use it as an identifier. String values are surrounded by double quotes; int - stores integers (whole numbers), without decimals, such as 123 or -123 If there is only one caller that needs this information, you can stop there. Primitive values do not share state with other primitive values. With an object array, we can return many different types of ... and a name (a String). Is Java “pass-by-reference” or “pass-by-value”? doing two different things). Now, lets learn about return type of a method in java. Yes, the language spec defines that "2" is the result. It's shockingly bad practice to write code like that, don't ever do it :). You are creating a coupling in the producer method to the consuming method that doesn't need to exist. You could easily implement it yourself though. The possible ways I can think of are: return a HashMap (since the two Objects are related) or return an ArrayList of Object objects. return can be used with methods in two ways: Methods returning a value : For methods that define a return type, return statement must be immediately followed by return value. The idea is to return an instance of a class containing all fields we want to return. No, you don't have two return types.It's a generic method you are seeing. You can choose to implement the construction of the name in the method that produces the list. Below is the class that acts as a wrapper that contain multiple data types. Note: Complied using JDK 1.7 & Decompiled using Cavaj. Below is a Java program to demonstrate the same. Although it may be almost as efficient (and simpler) to simply delay calculation of the names until the first time the method is called and store it then (lazy loading). Data type double is larger than char, hence, double return type is large enough to hold a char value and return it from the method. It's no different really from putting a public method into a private class. Multiple return values are fantastic, but Java as a language doesn’t really need them. How do I avoid a useless return in a Java method? Eclipse, for example, will claim that the return block will never be executed, but it's wrong. public static ReturningValues myMethod() { ReturningValues rv = new ReturningValues(); rv.setValue("value"); rv.setIndex(12); return rv; } Java doesn’t support multi-value returns. For instance: I know it's a bit ugly, but it works, and you just have to define your tuple types once. Does a finally block always get executed in Java? This should cover most of your needs, since in most situations one value is created before the other and you can split creating them in two methods. The drawback is that method createThingsB has an extra parameter comparing to createThings, and possibly you are passing exactly the same list of parameters twice to different methods. You have no extra dependencies and while there is a little extra calculation involved, you've avoided making your construction method too specific. After reading the ByteCode of program, the code is as follows: The finally block statements is inlined before the return statement of try block, so the return from the finally block executes first and the original return statement never does. To see how return values and a return types work in a real Java program, check out the code below.This code shows a method that returns a valueimportjava.text.NumberFormat;import static java.lang.System.out;classGoodAccount {String lastName;int id;double balance; double getInterest(double rate) {double interest;out.print(\"Adding \");out.print(rate);out.println(\… It returns 3 values—2 ints and a String. Can we overload a method based on different return type but same argument type and number, in java? Then return an instance of this list and call the name generation method as needed. If multiple return types are desired, then this would be a call break up these pieces of data into different methods calls or wrap these types in a custom object. Valid types are byte, short, int and long. EDIT: David Hanak's example is more elegant, as it avoids defining getters and still keeps the object immutable. javac uses this fact to implement covariant return types. I think this puts the responsibility for the creation of the names with the class that is most closely related to the objects themselves. The possible ways I can think of are: return a HashMap (since the two Objects are related) or return an ArrayList of Object objects. If you know you are going to return two objects, you can also use a generic pair: Edit A more fully formed implementation of the above: Notes, mainly around rustiness with Java & generics: In C++ (STL) there is a pair class for bundling two objects. Full signature includes return type in addition to argument types. These results objects are intimately tied together/related and belong together, or: they are unrelated, in which case your function isn't well defined in terms of what it's trying to do (i.e. two - java return multiple values of different types . Floating point types represents numbers with a fractional part, containing one or more decimals. ... You have some variables that are different types in Java language like that: ... key based on two objects of different type. Other callers may not need the extra information and you would be calculating extra information for these callers. You could do that by returning an array, which is an ugly way to solve it. It’s not really about returning two things from a function, it’s about the way your code is structured. int,double,char,string etc, In this approach we make a use of a string that is very unlikely to occur generally. Value Types would be memory-efficient, comparable with a C/C++ ‘struct’, and likely to take no more memory … It is used to exit from a method, with or without a value. Do the language specifications define the return value of a call to test()? How do I declare and initialize an array in Java? In this tutorial, we'll learn different ways to return multiple values from a Java method. objects - java return multiple values of different types AsyncTask's get() method: Is there any scenario where it is actually the best option? How do I address unchecked cast warnings? In other words: Is it always the same in every JVM? Can do some thing like a tuple in dynamic language (Python). How to return multiple objects ... D. Knuth. The reverse is also allowed but only when the method's return type is a wrapper of the same type as the type of the primitive value being returned - If you add/remove an object, you need only remove the calculated value and have it get recalculated on the next call. Certainly NetBeans gives you the warning "Exporting non-public type through public API" when you try to do this. Simply. Make the class smart enough that it constructs the name string on the fly as objects are added and removed from it. Java return ExamplesUse the return keyword in methods. How to remove the last character from a string? If a VM does it differently, it's not spec-compliant. I want to return these two Objects from one method because I dont want to iterate through the list of objects to get the comma separated names (which I can do in the same loop in this method). Yes, the Java Language Specification is very clear on this issue (14.20.2): A try statement with a finally block is executed by first executing the try block. The argument can be a primitive data type, String, etc. Then, we'll show how to use container classes for complex data and learn how to create generic tuple classes. So in your example, the return value will be 2. JVM uses full signature of a method for lookup/resolution. We have learned what is method in java with Syntax and definition already in previous post and have learned basics about it. This article explains the procedure for creating, exposing, and invoking a Web service with multiple return values in detail. If needed you can return multiple values using array or an object. To return multiple values in J, you return an array which contains multiple values. Then there is a choice: two - java return multiple values of different types. It seems to me that either: I see this sort of issue crop up again and again. Java 8 Object Oriented Programming Programming When a class has two or more methods by the same name but different parameters, at the time of calling based on the parameters passed respective method is called (or respective method body will be bonded with the calling line … We should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil. In the return expression, the two numbers are multiplied. Variables are containers for storing data values. You can return only one value in Java. For instance, if the return type of some method is boolean, we can not return an integer. Lastly, you could have the list itself be responsible for creating the name. How to get an enum value from a string value in Java? @# and I recommend regenerating the comma-separated list from the returned List. The code will end up being a lot cleaner. Java Variables. It’s built in a way that demands their absence. Please, do tell me if I have posted this question to the right subforum; become acclimated to the Coderanch environment. And Then using this string we will retrieve all the information required, that can be of diffrent types as well, Following code will Show the working of this concept, The separator used is ! How do I call one constructor from another in Java? Value Types. Using Pair (If there are only two returned values) We can use Pair in Java to return two values. i.e., a class can have two or more methods differing only by return type. In Java, there are different types of variables, for example: String - stores text, such as "Hello". Fastest way to determine if an integer's square root is an integer. This is the route I would go if the calculation needs to be done by more than one caller. Most obvious solution ever and a simplified version of case one. First, we'll return arrays and collections. ... (i.e. The eight primitive data types supported by the Java programming language are: byte: The byte data type is an 8-bit signed two's complement integer. This is the choice you've chosen, but I don't think it is the best one. // a java program to demonstrate that we can return multiple values of different types by making a class// and returning an object of class.// a class that stores and returns two members of different typesclass test{int mul; // to store multiplicationdouble div; // to store divisiontest(int m, double d){mul = m;div = d;}}class demo{static test getmultanddiv(int a, int b){// returning multiple values of … Where you call the routine that returns multiple values you code: PASS A HASH INTO THE METHOD AND POPULATE IT...... public void buildResponse(String data, Map response); Regarding the issue about multiple return values in general I usually use a small helper class that wraps a single return value and is passed as parameter to the method: (for primitive datatypes I use minor variations to directly store the value). This is a good trade-off. Value types are intended to be a third form of data type available in some future version of Java, to complement the currently-existing two: primitive types, and object references. I want to return two objects from a Java method and was wondering what could be a good way of doing so? A floating-point value cannot be returned from a method with an integer return type. How do you return multiple values in Python? How do I convert a String to an int in Java? Example. The type of data returned by a method must be compatible with the return type specified by the method. Advantages (in comparison to other solutions proposed): This is not exactly answering the question, but since every of the solution given here has some drawbacks, I suggest to try to refactor your code a little bit so you need to return only one value. create a class call ReturningValues. We can use following solutions to return multiple values. Tuples are something Java really lacks. Don't be afraid to create your own container/result classes that contain the data and the associated functionality to handle this. Finally, we'll see examples of how to use third-party libraries to return multiple values. Somehow, returning a HashMap does not look a very elegant way of doing so. If returned elements are of different types. Why not calculate it outside and pass it to the method? To make it more useful, these two methods can share some common logic: While in your case, the comment may be a good way to go, in Android, you can use Pair . In the Sun JVM the return value is 2, but I want to be sure, that this is not VM-dependant. two - java return multiple values of different types Multiple returns: Which one sets the final return value? How to generate random integers within a specific range in Java? We call it as a separator. To be more precise, the two objects I want to return are (a) List of objects and (b) comma separated names of the same. I am reading a file and generating two arrays, of type String and int from it, picking one element for both from each line. A primitive type is predefined by the language and is named by a reserved keyword. This separator would be used to separate various values when used in a function, For example we will have our final return as (for example) intValue separator doubleValue separator... I have a been using a very basic approach to deal with problems of multiple returns. In Java Generics a pair class isn't available, although there is some demand for it. Most compilers will complain about it. ... To return two values, we can use a class argument—then we set values within that class. You need something inside as well as outside of your method. You do not have to create a special class declaration for individual methods and its return types, The parameters get a name and therefore are easier to differentiate when looking at the method signature. In the example given below the calculate() method accepts two integer variables performs the addition subtraction, multiplication and, division operations on them stores the results in an array and returns the array. Primitive number types are divided into two groups: Integer types stores whole numbers, positive or negative (such as 123 or -456), without decimals. Syntax of method in Java The variable receiving the value returned by a method must also be compatible with the return type … There is no loss in the value of char even if its value is widened to a double. 2. It's not always possible, but maybe both of the values can be created independently of each other? (4) Fastest way to determine if an integer's square root is an integer. Suppose that you have a method and you want it to return two values instead of one. I’m primarily a Perl hacker but I’ve done some lisp, too. We can return an array in Java. two - java return multiple values of different types, https://commons.apache.org/proper/commons-lang/apidocs/org/apache/commons/lang3/tuple/package-summary.html. The aim of this article is to explain ways to return multiple values from a Web service operation. In Java we must use a class instance, an array or other collection to return these values. These have long been of interest to enable Java functions to return multiple (tuple) results, and for scientific & graphics calculation efficiency. Why not create a WhateverFunctionResult object that contains your results, and the logic required to parse these results, iterate over then etc. ... ComputeSize This method receives two arguments, both of type int. As I see it there are really three choices here and the solution depends on the context. This class can be a POJO with public member variables and a public constructor to initiate its fields with required values or a JavaBean with corresponding getters and setters for their private member variables and no-arg public constructor. < E extends Foo >--> you are declaring a generic type for your method List < E >--> this is your return type Your method can have a generic type E which is a sub-class of Foo. Java - valueOf() Method - The valueOf method returns the relevant Number Object holding the value of the argument passed. what about returning 3 instead of 2 values, changing type of some field etc.) Since the only data type in J is array (this is an oversimplification, from some perspectives - but those issues are out of scope for this task), this is sort of like asking how to return only one value in another language. How do you return multiple values in Python? This is the most commonly used method to return multiple values from a method in Java. I almost always end up defining n-Tuple classes when I code in Java. If all returned elements are of same type. All possible solutions will be a kludge (like container objects, your HashMap idea, “multiple return values” as realized via arrays). public class ReturningValues { private String value; private int index; // getters and setters here } and change myMethod () as follows. Tip 2 An object instance can be passed to the method, which then just sets fields. 3 values are being returned intVal,doubleVal and stringVal. The method returns these two values. Coming to Java from a more functional language can be a mind shift in this way, but in Java's case it's a shift that makes sense when thinking about how the language works. (6) At first I tried a constructor that would take in multiple return values.then I hit a wall. If you simply pass the stuff around in a HashMap or similar, then your clients have to pull this map apart and grok the contents each time they want to use the results. There are two ways of doing this; they are: Return type can be a Complex Data type with muliple parts or arrays. A method that wants to return multiple values would then be declared as follows: Maybe the major drawback is that the caller has to prepare the return objects in advance in case he wants to use them (and the method should check for null pointers). This example accepts an ArrayList and a message text from a databasehelper getInfo. I need to create a hashmap with key as integer and it should hold multiple values of different data types. In the latter case, my solution would be to create a specialized List class that returns a comma-separated string of the names of objects that it contains. It serves the purpose, and avoids complexity. How to determine whether an array contains a particular value in Java? Which type you should use, depends on the numeric value. If execution of the try block completes normally, [...], If execution of the try block completes abruptly because of a throw of a value V, [...], If the finally block completes normally, [...]. your return type is a List
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