Misconceptions

These are the misconceptions we collected so far in:

There is no connection between the number of misconceptions listed here and the difficulty of the corresponding programming language. The effort we spent on collecting misconceptions is very different for different languages. It would be inappropriate to reason about the quality of languages based on the number of misconceptions in this collection.

AddMemberAtRuntime

AddMemberAtRuntime

Set of class members can change at runtime

ArithmeticPlusPrecedes

ArithmeticPlusPrecedes

Addition has higher precedence than string concatenation

ArrayHasLengthMethod

ArrayHasLengthMethod

To get the length of an array, one needs to call its length method

ArrayListIsArray

ArrayListIsArray

ArrayLists are arrays

ArraysGrow

ArraysGrow

Arrays can grow dynamically

AssignCompares

AssignCompares

= compares two values

AssignmentCopiesObject

AssignmentCopiesObject

Assignment copies the object

AssignmentNotExpression

AssignmentNotExpression

An assignment a=b is not an expression

CallNotStaticallyChecked

CallNotStaticallyChecked

A method invocation on a reference of a type that does not have that method won't compile

CannotChainMemberAccesses

CannotChainMemberAccesses

Member accesses cannot be chained together

CannotChainMemberToConstructor

CannotChainMemberToConstructor

Method calls or field accesses cannot be chained to a constructor invocation

CharNotNumeric

CharNotNumeric

Char is not a numeric type

ComparisonWithBooleanLiteral

ComparisonWithBooleanLiteral

To test whether an expression is true or false, one must compare it to true or to false

ConditionalIsSequence

ConditionalIsSequence

If-else is equivalent to sequence of two ifs

ConstructorAllocates

ConstructorAllocates

The constructor allocates the object

ConstructorReturnsObject

ConstructorReturnsObject

Constructors need to return objects

ControlledLocalAccess

ControlledLocalAccess

One can control access to local variables using access modifiers

DeferredReturn

DeferredReturn

A return statement in the middle of a method doesn't return immediately

EqualityOperatorComparesObjectsValues

EqualityOperatorComparesObjectsValues

o==p compares the objects referred to by variables o and p

EqualsComparesReferences

EqualsComparesReferences

o.equals(p) compares the references stored in the variables o and p

FinalReferenceImpliesImmutability

FinalReferenceImpliesImmutability

An object referred to by a final variable is an immutable object

IfIsLoop

IfIsLoop

The body of an if statement executes repeatedly, as long as the condition holds

LargeIntegerLong

LargeIntegerLong

Large integer numbers have type long

LocalVariablesAutoInitialized

LocalVariablesAutoInitialized

Local variables are automatically initialized

MapToBooleanWithConditionalOperator

MapToBooleanWithConditionalOperator

To map a boolean expression to a boolean, a conditional operator is necessary

MapToBooleanWithIf

MapToBooleanWithIf

To map a boolean expression to a boolean, an if statement is necessary

MustInitializeFieldInConstructor

MustInitializeFieldInConstructor

Constructors must assign values to all fields

NoAtomicExpression

NoAtomicExpression

Expressions must consist of more than one piece

NoEmptyConstructor

NoEmptyConstructor

A constructor must do something

NoFloatLiterals

NoFloatLiterals

There are no float literals

NoLongLiterals

NoLongLiterals

There are no long literals

NoReservedWords

NoReservedWords

Every sequence of letters and digits starting with a letter can be used as an identifier

NoShortCircuit

NoShortCircuit

&& and || always evaluate both operands

NoSingleLogicAnd

NoSingleLogicAnd

& is only a bitwise AND

NullIsObject

NullIsObject

null is an object

ObjectsMustBeNamed

ObjectsMustBeNamed

A variable is needed to instantiate an object

OutsideInMethodNesting

OutsideInMethodNesting

Nested method calls are invoked outside in

ParenthesesOnlyIfArgument

ParenthesesOnlyIfArgument

() are optional for method calls without arguments

PrivateFromOtherInstance

PrivateFromOtherInstance

An object cannot access private members of other objects of the same class

PrivateFromStatic

PrivateFromStatic

Static methods cannot access private members of instances of same class

RecursiveActivationsShareFrame

RecursiveActivationsShareFrame

Recursive calls of a method share a stack frame

RecursiveMethodImpliesRecursiveType

RecursiveMethodImpliesRecursiveType

A class with a recursive method represents part of a recursive data structure

RecursiveMethodNeedsIfElse

RecursiveMethodNeedsIfElse

A recursive method needs to contain an if-else statement

ReferenceToVariable

ReferenceToVariable

References can point to variables

ReturnCall

ReturnCall

Return statements need () around the return value

ReturnUnwindsMultipleFrames

ReturnUnwindsMultipleFrames

A return statement can unwind multiple call stack frames

RightToLeftChaining

RightToLeftChaining

Chained accesses are invoked from right to left

StringLiteralNoObject

StringLiteralNoObject

One needs to call the String constructor to get a String object from a literal

StringPlusStringifiesExpression

StringPlusStringifiesExpression

String concatenation stringifies non-String operand expressions

ThisAssignable

ThisAssignable

One can assign to this

ThisCanBeNull

ThisCanBeNull

this can be null

ThisExistsInStaticMethod

ThisExistsInStaticMethod

this is a local variable, also in static methods

ThisNoExpression

ThisNoExpression

The name this is not an expression

VariablesHoldExpressions

VariablesHoldExpressions

= stores an expression in a variable

VariablesHoldObjects

VariablesHoldObjects

A variable of a reference type contains a whole object

Programming Language

Notional Machine

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