Summary

The primitive wrapper constructors are being deprecated for removal, they have been deprecated since JDK 9.

The classes with constructors to be deprecated for removal are java.lang.Boolean, java.lang.Byte, java.lang.Character, java.lang.Short, java.lang.Integer, java.lang.Long, java.lang.Float, and java.lang.Double.

Problem

The Valhalla project aims to unify the primitive and class-based type systems of Java by introducing primitive classes, whose instances lack identity. As part of this unification, the primitive wrapper classes will be repurposed so that rather than wrapping the existing primitive values, they will represent the primitive values directly—that is, the existing primitive values will be considered identity-free instances of these classes.

JEP 390 anticipates these changes by introducing warnings about code that may no longer work properly when certain classes of the Java Platform API, including the wrapper classes, become primitive classes.

In particular, while a primitive class has constructors, the semantics of those constructors are different: a unique identity is not produced with each invocation. Instead, instances whose fields have the same values are considered ==.

In addition, primitive class constructors are not encoded in class files using instance initialization methods. Existing binaries that attempt to invoke a method like Integer.<init>:(I)V will encounter LinkageErrors.

In the future, to minimize surprises due to these changes, the primitive wrapper constructors will be made private, and all clients will be required to get instances through literals, primitive operations, or the valueOf and parse* methods. These alternative methods never promise to produce an instance with a unique identity.

As a first step, the primitive wrapper constructors are being marked for removal.

Solution

The @Deprecated annotations will include "forRemoval = true". This will draw attention to the coming accessibility reduction and give clients an opportunity to update their code.

We expect most projects under active development will respond by updating their code (if they have not already). That said, usage of these constructors is widespread. For those projects or legacy binaries that don't get updated, we'll investigate tooling in a future release that will allow users to adapt to the removal by opting in to bytecode rewrites, replacing constructor calls with valueOf calls.

Specification

These constructors will be annotated to deprecate for removal.

@Deprecated(since="9", forRemoval = true)
public java.lang.Boolean(boolean) {...}

@Deprecated(since="9", forRemoval = true)
public java.lang.Boolean(java.lang.String) {...}

@Deprecated(since="9", forRemoval = true)
public java.lang.Byte(byte) {...}

@Deprecated(since="9", forRemoval = true) 
public java.lang.Byte(java.lang.String) throws java.lang.NumberFormatException {...}

@Deprecated(since="9", forRemoval = true)
public java.lang.Character(char) {...}

@Deprecated(since="9", forRemoval = true)
public java.lang.Short(short) {...}

@Deprecated(since="9", forRemoval = true)
public java.lang.Short(java.lang.String) throws java.lang.NumberFormatException {...}

@Deprecated(since="9", forRemoval = true)
public java.lang.Integer(int) {...}

@Deprecated(since="9", forRemoval = true)
public java.lang.Integer(java.lang.String) throws java.lang.NumberFormatException {...}

@Deprecated(since="9", forRemoval = true)
public java.lang.Long(long) {...}

@Deprecated(since="9", forRemoval = true)
public java.lang.Long(java.lang.String) throws java.lang.NumberFormatException {...}

@Deprecated(since="9", forRemoval = true)
public java.lang.Float(float) {...}

@Deprecated(since="9", forRemoval = true)
public java.lang.Float(double) {...}

@Deprecated(since="9", forRemoval = true)
public java.lang.Float(java.lang.String) throws java.lang.NumberFormatException {...}

@Deprecated(since="9", forRemoval = true)
public java.lang.Double(double) {...}

@Deprecated(since="9", forRemoval = true)
public java.lang.Double(java.lang.String) throws java.lang.NumberFormatException {...}