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Java

533The Object Class and toString's Default Behavior
534Why toString Matters: Debugging and Logging
535Overriding toString: Basic Syntax
536Formatting toString Output: Best Practices
537toString for Complex Objects: Nested References
538StringBuilder for Efficient toString Implementations
539IDE-Generated toString Methods
540toString in Collections and Arrays
541The equals Method: Reference vs Logical Equality
542Overriding equals: The Five Requirements
543Implementing equals: The Step-by-Step Recipe
544The hashCode Method: What It Returns
545The equals-hashCode Contract: Core Requirement
546Why hashCode Matters for Hash-Based Collections
547Implementing hashCode: Combining Field Hash Codes
548Objects.equals and Objects.hash Utility Methods
549Common equals and hashCode Mistakes
550equals and hashCode with Inheritance
551The Cantor Principle: Why the Contract Is Not Bidirectional
552IDE Generation and Records: Automatic Implementation
553The HashMap Contract: equals and hashCode Must Agree
554How HashMap Uses hashCode for Bucket Selection
555Duplicate Keys with Broken hashCode: The Problem
556The Lookup Failure: Finding Keys That Exist
557Demonstrating the Bug: A Step-by-Step Example
558HashSet Breakage: The Same Root Cause
559The equals-hashCode Contract in Detail
560Fixing the Bug: Implementing Both Methods Correctly
561The Cloneable Interface and Object.clone
562Default clone Behavior: Shallow Copying
563Implementing clone: Overriding and CloneNotSupportedException
564Shallow Copy Problem: Shared References
565Deep Copying: Cloning Referenced Objects
566Deep Copy Example: Arrays and Collections
567Clone and Inheritance: Calling super.clone
568When Not to Use clone: Alternatives
569Final Fields and clone: The Conflict
570Clone Best Practices and Common Pitfalls
571The getClass Method: Runtime Type Information
572Using getClass for Type Comparison
573Class Objects and Reflection Entry Point
574The finalize Method: Legacy Cleanup Mechanism
575Problems with finalize: Unpredictability and Performance
576Modern Alternatives to finalize
577Deprecation of finalize in Java 9+

Java

533The Object Class and toString's Default Behavior
534Why toString Matters: Debugging and Logging
535Overriding toString: Basic Syntax
536Formatting toString Output: Best Practices
537toString for Complex Objects: Nested References
538StringBuilder for Efficient toString Implementations
539IDE-Generated toString Methods
540toString in Collections and Arrays
541The equals Method: Reference vs Logical Equality
542Overriding equals: The Five Requirements
543Implementing equals: The Step-by-Step Recipe
544The hashCode Method: What It Returns
545The equals-hashCode Contract: Core Requirement
546Why hashCode Matters for Hash-Based Collections
547Implementing hashCode: Combining Field Hash Codes
548Objects.equals and Objects.hash Utility Methods
549Common equals and hashCode Mistakes
550equals and hashCode with Inheritance
551The Cantor Principle: Why the Contract Is Not Bidirectional
552IDE Generation and Records: Automatic Implementation
553The HashMap Contract: equals and hashCode Must Agree
554How HashMap Uses hashCode for Bucket Selection
555Duplicate Keys with Broken hashCode: The Problem
556The Lookup Failure: Finding Keys That Exist
557Demonstrating the Bug: A Step-by-Step Example
558HashSet Breakage: The Same Root Cause
559The equals-hashCode Contract in Detail
560Fixing the Bug: Implementing Both Methods Correctly
561The Cloneable Interface and Object.clone
562Default clone Behavior: Shallow Copying
563Implementing clone: Overriding and CloneNotSupportedException
564Shallow Copy Problem: Shared References
565Deep Copying: Cloning Referenced Objects
566Deep Copy Example: Arrays and Collections
567Clone and Inheritance: Calling super.clone
568When Not to Use clone: Alternatives
569Final Fields and clone: The Conflict
570Clone Best Practices and Common Pitfalls
571The getClass Method: Runtime Type Information
572Using getClass for Type Comparison
573Class Objects and Reflection Entry Point
574The finalize Method: Legacy Cleanup Mechanism
575Problems with finalize: Unpredictability and Performance
576Modern Alternatives to finalize
577Deprecation of finalize in Java 9+

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Lesson 553 of 2,870·13. The Object Class and Common MethodsPro lesson

The HashMap Contract: equals and hashCode Must Agree

Learn why HashMap requires both equals and hashCode to be consistent for correct behavior.

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