Does Java support structs?

Does Java have an analog of a C++ struct:

struct Member { string FirstName; string LastName; int BirthYear; }; 

I need to use my own data type.

11 Answers

The equivalent in Java to a struct would be

class Member { public String firstName; public String lastName; public int birthYear; }; 

and there's nothing wrong with that in the right circumstances. Much the same as in C++ really in terms of when do you use struct versus when do you use a class with encapsulated data.

Java definitively has no structs :) But what you describe here looks like a JavaBean kind of class.

Java 14 has added support for Records, which are structured data types that are very easy to build.

You can declare a Java record like this:

public record AuditInfo( LocalDateTime createdOn, String createdBy, LocalDateTime updatedOn, String updatedBy ) {} public record PostInfo( Long id, String title, AuditInfo auditInfo ) {} 

And, the Java compiler will generate the following Java class associated to the AuditInfo Record:

public final class PostInfo extends java.lang.Record { private final java.lang.Long id; private final java.lang.String title; private final AuditInfo auditInfo; public PostInfo( java.lang.Long id, java.lang.String title, AuditInfo auditInfo) { /* compiled code */ } public java.lang.String toString() { /* compiled code */ } public final int hashCode() { /* compiled code */ } public final boolean equals(java.lang.Object o) { /* compiled code */ } public java.lang.Long id() { /* compiled code */ } public java.lang.String title() { /* compiled code */ } public AuditInfo auditInfo() { /* compiled code */ } } public final class AuditInfo extends java.lang.Record { private final java.time.LocalDateTime createdOn; private final java.lang.String createdBy; private final java.time.LocalDateTime updatedOn; private final java.lang.String updatedBy; public AuditInfo( java.time.LocalDateTime createdOn, java.lang.String createdBy, java.time.LocalDateTime updatedOn, java.lang.String updatedBy) { /* compiled code */ } public java.lang.String toString() { /* compiled code */ } public final int hashCode() { /* compiled code */ } public final boolean equals(java.lang.Object o) { /* compiled code */ } public java.time.LocalDateTime createdOn() { /* compiled code */ } public java.lang.String createdBy() { /* compiled code */ } public java.time.LocalDateTime updatedOn() { /* compiled code */ } public java.lang.String updatedBy() { /* compiled code */ } } 

Notice that the constructor, accessor methods, as well as equals, hashCode, and toString are created for you, so it's very convenient to use Java Records.

A Java Record can be created like any other Java object:

PostInfo postInfo = new PostInfo( 1L, "High-Performance Java Persistence", new AuditInfo( LocalDateTime.of(2016, 11, 2, 12, 0, 0), "Vlad Mihalcea", LocalDateTime.now(), "Vlad Mihalcea" ) ); 

Actually a struct in C++ is a class (e.g. you can define methods there, it can be extended, it works exactly like a class), the only difference is that the default access modfiers are set to public (for classes they are set to private by default).

This is really the only difference in C++, many people don't know that. ; )

Java doesn't have an analog to C++'s structs, but you can use classes with all public members.

Yes, Java doesn't have struct/value type yet. But, in the upcoming version of Java, we are going to get inline class which is similar to struct in C# and will help us write allocation free code.

 inline class point { int x; int y; } 

With Project JUnion you can use structs in Java by annotating a class with @Struct annotation

@Struct class Member { string FirstName; string LastName; int BirthYear; } 

More info at the project's website:

Yes, a class is what you need. An class defines an own type.

Structs "really" pure aren't supported in Java. E.g., C# supports struct definitions that represent values and can be allocated anytime.

In Java, the unique way to get an approximation of C++ structs

struct Token { TokenType type; Stringp stringValue; double mathValue; } // Instantiation { Token t = new Token; } 

without using a (static buffer or list) is doing something like

var type = /* TokenType */ ; var stringValue = /* String */ ; var mathValue = /* double */ ; 

So, simply allocate variables or statically define them into a class.

Along with Java 14, it starts supporting Record. You may want to check that

public record Person (String name, String address) {} Person person = new Person("Esteban", "Stormhaven, Tamriel"); 

And there are Sealed Classes after Java 15.

sealed interface Shape permits Circle, Rectangle { record Circle(Point center, int radius) implements Shape { } record Rectangle(Point lowerLeft, Point upperRight) implements Shape { } } 

The short answer: NO.

The long answer:

1. The main different between class and struct (in C++) is all properties in struct is public, which can be accessed from anywhere. For the class, you can apply limit it with different level of privacy.
2. If you wanna have a data structure same as struct in C++, just make all properties public.