Package Torello.Java.Additional

Class ConstantPool.Reference

java.lang.Object

Torello.Java.Additional.ConstantPool.Reference

Enclosing class:

ConstantPool

public static class ConstantPool.Reference
extends java.lang.Object

A Data-Class which can represent:

• ConstantPool.TAG_FIELD_REF (9)
• ConstantPool.TAG_METHOD_REF (10)
• ConstantPool.TAG_INTERFACE_METHOD_REF (11)

Example Java Constant-Pool Table:
The following table was (partially) put together by none other than the illustrious Chat-GPT on December 17th, 2024. This table does not actually contain everything that can / does go into a typical Constant-Table, but rather only the constants which are pertinent to this example are included in this, example, table.

Admittedly, I ended up adding all kinds of stuff to the table, and changing around some of the text, but, when your brain isn't working so well, A.I. will help you tremendously come up with stuff. "Writer's Block" (starting at a blank screen) is a real phenomenon when programming.

Chat-GPT never ceases to amaze me.

Index	Tag-Kind	Tag-Kind Name	Value
1	1	UTF8	`toString`
2	7	Class	Index-Pointer: 10 → Points to [`UTF8`, "MyClass"]
3	12	NameAndType	Index-Pointer: 1 → Points to [`UTF8`, "toString"] Index-Pointer: 9 → Points to [`UTF8`, "()Ljava/lang/String;"]
4	1	UTF8	`equals`
5	12	NameAndType	Index-Pointer: 4 → Points to [`UTF8`, "equals"] Index-Pointer: 8 → Points to [`UTF8`, "(Ljava/lang/Object;)Z"]
6	7	Class	Index-Pointer: 11 → Points to [`UTF8`, "java/lang/Object"]
7	10	MethodRef	Index-Pointer: 2 → Points to a [`Class` Entry] Index-Pointer: 3 → Points to a [`NameAndType` Entry]
8	1	UTF8	`(Ljava/lang/Object;)Z`
9	1	UTF8	`()Ljava/lang/String;`
10	1	UTF8	`MyClass`
11	1	UTF8	`java/lang/Object`
12	9	MethodRef	Index-Pointer: 6 → Points to a [`Class` Entry] Index-Pointer: 5 → Points to a [`NameAndType` Entry]

Method-Reference Entries / Records:

Method-Reference for toString() is a Pointer-Pair located @ Table-Index 7:

• Index 2 → Points to a [Class Entry], which is another Index-Pointer to →
  
  • Index 10: which contains a [UTF-8 Entry] "MyClass"
• Index 3 → Points to a [Name-And-Type Entry], which is another Pointer-Pair to →
  • Index 1: (Name), which contains a [UTF-8 Entry] "toString"
  • Index 9: (Type), which contains a [UTF-8 Entry] "()Ljava/lang/String;"

Method-Reference for equals() is a Pointer-Pair located @ Table-Index 12:

• Index 6 → Points to a [Class Entry], which is another Index-Pointer to →
  
  • Index 11: which contains a [UTF-8 Entry] "java/lang/Object"
• Index 5 → Points to a [Name-And-Type Entry], which is another Pointer-Pair to →
  • Index 4: (Name), which contains a [UTF-8 Entry] "equals"
  • Index 8: (Type), which contains a [UTF-8 Entry] "(Ljava/lang/Object;)Z"

Instances of 'ConstantPool.Reference':

ConstantPool.Reference Field	Assigned Value
tag	10 (TAG_METHOD_REF)
tableIndex	7
name	"toString"
ownerClassName	"MyClass"
descriptor	"()Ljava/lang/String;"
descriptorUTF8Index	9
nameAndTypeIndex	3
nameUTF8Index	1
ownerClassIndex	2
ownerClassNameUTF8Index	10

ConstantPool.Reference Field	Assigned Value
tag	10 (TAG_METHOD_REF)
tableIndex	12
name	"equals"
ownerClassName	"java/lang/Object"
descriptor	"(Ljava/lang/Object;)Z"
descriptorUTF8Index	8
nameAndTypeIndex	5
nameUTF8Index	4
ownerClassIndex	6
ownerClassNameUTF8Index	11

Hi-Lited Source-Code:

• View Here: Torello/Java/Additional/ConstantPool.java
• Open New Browser-Tab: Torello/Java/Additional/ConstantPool.java

File Size: 10,345 Bytes Line Count: 256 '\n' Characters Found

Field Summary

Either TAG_FIELD_REF (9) or TAG_METHOD_REF (10) or TAG_INTERFACE_METHOD_REF (11)
Modifier and Type	Field	Description
byte	tag	The Constant-Pool Tg-Kind associated with this instance.
Reference's Actual Table-Index in the Constant-Pool
Modifier and Type	Field	Description
int	tableIndex	The Constant-Pool Table-Index where this Reference is located
UTF-8 Name-String Reference Data
Modifier and Type	Field	Description
String	name	This is just the name of the Method or Field.
String	ownerClassName	The 'className' field specifies in which class (where) the Method or Field has actuallly been defined.
UTF-8 Method or Field Descriptor, as a String
Modifier and Type	Field	Description
String	descriptor	This is the descriptor of a method or field, which is Java single-line description which includes type-information stored as a simple String.
Constant-Pool Table-Entry Indices
Modifier and Type	Field	Description
int	descriptorUTF8Index	Constant-Pool Table-Index identifying where the UTF-8 Descriptor's Description-As-A-String is located.
int	nameAndTypeIndex	An intermediate Constant-Pool Index-Pair that points to a Name UTF-8 Constant, and a Type-Descriptor Constant.
int	nameUTF8Index	Constant-Pool Table-Index identifying where the UTF-8 Method's or Field's Name-As-A-String is located.
int	ownerClassIndex	Constant-Pool Table-Index where owner's className 'Class Constant' was stored
int	ownerClassNameUTF8Index	Constant-Pool Table-Index identifying where the UTF-8 Class' Name-As-A-String is located.

Method Summary

Methods: class java.lang.Object
Modifier and Type	Method	Description
boolean	equals(Object other)	Checks for Object-equality between 'this' instance and 'other'.
int	hashCode()	Generates a Hash-Code.
String	toString()	Converts instance into a String.

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

tableIndex

🡇 ⇈ ⮫ 🗕 🗗 🗖

public final int tableIndex

The Constant-Pool Table-Index where this Reference is located

Code:

Exact Field Declaration Expression:

 public final int tableIndex;

tag

🡅 🡇 ⇈ ⮫ 🗕 🗗 🗖

public final byte tag

The Constant-Pool Tg-Kind associated with this instance. This Java 'byte' may take only one of only three values:

• ConstantPool.TAG_FIELD_REF (9)
• ConstantPool.TAG_METHOD_REF (10)
• ConstantPool.TAG_INTERFACE_METHOD_REF (11)

The "Tag-Kind" for any Constant in a Java '.class' File's Constant-Pool are a byte-Value which occupies the first byte of the constant's definition in the byte[]-Array which was loaded from disk.

Code:

Exact Field Declaration Expression:

 public final byte tag;

ownerClassName

🡅 🡇 ⇈ ⮫ 🗕 🗗 🗖

public final java.lang.String ownerClassName

The 'className' field specifies in which class (where) the Method or Field has actuallly been defined. For most methods and fields, the 'className' is the same as the actual class whose Constant-Pool was loaded into an instance of ConstantPool.

If the field or method reference is defined in an ancestor or parent class, then this field would contain the name of that ancestor.

Code:

Exact Field Declaration Expression:

 public final String ownerClassName;

ownerClassIndex

🡅 🡇 ⇈ ⮫ 🗕 🗗 🗖

public final int ownerClassIndex

Constant-Pool Table-Index where owner's className 'Class Constant' was stored

Code:

Exact Field Declaration Expression:

 public final int ownerClassIndex;

ownerClassNameUTF8Index

🡅 🡇 ⇈ ⮫ 🗕 🗗 🗖

public final int ownerClassNameUTF8Index

Constant-Pool Table-Index identifying where the UTF-8 Class' Name-As-A-String is located.

Code:

Exact Field Declaration Expression:

 public final int ownerClassNameUTF8Index;

nameAndTypeIndex

🡅 🡇 ⇈ ⮫ 🗕 🗗 🗖

public final int nameAndTypeIndex

An intermediate Constant-Pool Index-Pair that points to a Name UTF-8 Constant, and a Type-Descriptor Constant.

Code:

Exact Field Declaration Expression:

 public final int nameAndTypeIndex;

name

🡅 🡇 ⇈ ⮫ 🗕 🗗 🗖

public final java.lang.String name

This is just the name of the Method or Field. Some common method names are (just for example) and 'equals'. This particular Nested-Type has three fields of it's own, named: 'className, 'name' and 'descriptor'.

Code:

Exact Field Declaration Expression:

 public final String name;

nameUTF8Index

🡅 🡇 ⇈ ⮫ 🗕 🗗 🗖

public final int nameUTF8Index

Constant-Pool Table-Index identifying where the UTF-8 Method's or Field's Name-As-A-String is located.

Code:

Exact Field Declaration Expression:

 public final int nameUTF8Index;

descriptor

🡅 🡇 ⇈ ⮫ 🗕 🗗 🗖

public final java.lang.String descriptor

This is the descriptor of a method or field, which is Java single-line description which includes type-information stored as a simple String. A descriptor is of the format:

• For a method, the descriptor specifies the parameter types and return type.
• For a field, the descriptor specifies the field type.

Code:

Exact Field Declaration Expression:

 public final String descriptor;

descriptorUTF8Index

🡅 🡇 ⇈ ⮫ 🗕 🗗 🗖

public final int descriptorUTF8Index

Constant-Pool Table-Index identifying where the UTF-8 Descriptor's Description-As-A-String is located.

Code:

Exact Field Declaration Expression:

 public final int descriptorUTF8Index;

Method Detail

toString

🡅 🡇 ⇈ ⮫ 🗕 🗗 🗖

public final java.lang.String toString()

Converts instance into a java.lang.String.

Overrides:

toString in class java.lang.Object

Returns:

The data-content of this record, as a String, for printing.

Code:

Exact Method Body:

 return
     "Reference:\n" +
     "{\n" +
     "    tag:             " + tag + " - " + ConstantPool.tagNames.get(tag) + '\n' +
     "    Table-Index:     " + this.tableIndex + '\n' +                
     "    ownerClassName:  " + this.ownerClassName + '\n' +
     "    name:            " + this.name + '\n' +
     "    descriptor:      " + this.descriptor + '\n' +
     "}";

equals

🡅 🡇 ⇈ ⮫ 🗕 🗗 🗖

public boolean equals(java.lang.Object other)

Checks for Object-equality between 'this' instance and 'other'.

Overrides:

equals in class java.lang.Object

Parameters:

other - This may be any Java-Object, but only an instance of ConstantPool.Reference will permit this method to return TRUE.

Returns:

TRUE if-and-only-if parameter 'other' is an instance of Reference and has identical field values.

Code:

Exact Method Body:

 if (!(other instanceof Reference)) return false;

 Reference r = (Reference) other;

 return
         (this.tag == r.tag)

     &&  Objects.equals(this.ownerClassName, r.ownerClassName)
     &&  (this.ownerClassIndex           == r.ownerClassIndex)
     &&  (this.ownerClassNameUTF8Index   == r.ownerClassNameUTF8Index)

     &&  Objects.equals(this.name, r.name)
     &&  (this.nameUTF8Index == r.nameUTF8Index)

     &&  Objects.equals(this.descriptor, r.descriptor)
     &&  (this.descriptorUTF8Index == r.descriptorUTF8Index);

hashCode

🡅 ⇈ ⮫ 🗕 🗗 🗖

public int hashCode()

Generates a Hash-Code.

Overrides:

hashCode in class java.lang.Object

Returns:

An integer Hash-Code that may be used by Java's Hashing Data-Structures.

Code:

Exact Method Body:

 return this.name.hashCode() +
     this.ownerClassNameUTF8Index +
     this.nameUTF8Index +
     this.descriptorUTF8Index;