Misconceptions

Here are a couple of misconceptions. Many more to come...

The 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

Set of class members can change at runtime

ArithmeticPlusPrecedes

Addition has higher precedence than string concatenation

ArrayHasLengthMethod

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

ArrayListIsArray

ArrayLists are arrays

ArraysGrow

Arrays can grow dynamically

AssignCompares

= compares two values

AssignCompares

= compares two values

AssignmentCopiesObject

Assignment copies the object

AssignmentCopiesObject

Assignment copies the object

AssignmentCopiesObject

Assignment copies the object

AssignmentNotExpression

An assignment a=b is not an expression

CallNotStaticallyChecked

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

CannotChainAttributeToObjectInstantiation

Method calls, and attribute accesses in general, cannot be chained to a constructor invocation.

CannotChainMemberAccesses

Member accesses cannot be chained together

CannotChainMemberToConstructor

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

CharNotNumeric

Char is not a numeric type

ClassDefinesType

The type of an object is equivalent to the type defined by its class definition

ComparisonWithBoolLiteral

To test whether an expression is True or False, one must compare it to True or to False

ComparisonWithBooleanLiteral

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

ConditionalIsSequence

If-else is equivalent to sequence of two ifs

ConditionalIsSequence

If-else is equivalent to sequence of two ifs

ConstReferenceImpliesImmutability

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

ConstructorAllocates

The constructor allocates the object

ConstructorReturnsObject

Constructors need to return objects

ControlledLocalAccess

One can control access to local variables using access modifiers

DeferredReturn

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

DeferredReturn

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

EqualityOperatorComparesObjectsValues

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

EqualsComparesReferences

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

FinalReferenceImpliesImmutability

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

IfIsLoop

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

IfIsLoop

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

InitCreates

__init__ must create a new object

InitReturnsObject

__init__ needs to return an object

LargeIntegerLong

Large integer numbers have type long

LocalVariablesAutoInitialized

Local variables are automatically initialized

MapToBooleanWithConditionalOperator

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

MapToBooleanWithIf

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

MapToBooleanWithIf

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

MapToBooleanWithTernaryOperator

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

MissingElseTerminates

Blocks following an if without else will not execute if the condition is false

MultipleValuesReturn

Functions can return multiple values

MustInitializeFieldInConstructor

Constructors must assign values to all fields

NoAtomicExpression

Expressions must consist of more than one piece

NoAtomicExpression

Expressions must consist of more than one piece

NoAtomicExpression

Expressions must consist of more than one piece

NoEmptyConstructor

A constructor must do something

NoEmptyInit

__init__ must do something

NoFloatLiterals

There are no float literals

NoLongLiterals

There are no long literals

NoReservedWords

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

NoReservedWords

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

NoShortCircuit

&& and || always evaluate both operands

NoShortCircuit

and/or always evaluate both operands

NoSingleLogicAnd

& is only a bitwise AND

NullIsObject

null is an object

NullIsObject

null is an object

ObjectsMustBeNamed

A variable is needed to instantiate an object

ObjectsMustBeNamed

A variable is needed to instantiate an object

OutsideInFunctionNesting

Nested function calls are invoked outside in

OutsideInMethodNesting

Nested method calls are invoked outside in

ParenthesesOnlyIfArgument

() are optional for method calls without arguments

ParenthesesOnlyIfArgument

() are optional for function calls without arguments

PrivateFromOtherInstance

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

PrivateFromStatic

Static methods cannot access private members of instances of same class

RecursiveActivationsShareFrame

Recursive calls of a method share a stack frame

RecursiveFunctionNeedsIfElse

A recursive function needs to contain an if-else statement

RecursiveMethodImpliesRecursiveType

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

RecursiveMethodNeedsIfElse

A recursive method needs to contain an if-else statement

ReferenceToVariable

References can point to variables

ResetStateEachLoopIteration

The computation of all loop iterations starts from the state before the loop

ResetStateEachProgramExecution

Running a Scratch program first resets the state of the world and then executes the program

ReturnCall

Return statements need () around the return value

ReturnCall

Return statements need () around the return value

ReturnUnwindsMultipleFrames

A return statement can unwind multiple call stack frames

ReturnUnwindsMultipleFrames

A return statement can unwind multiple call stack frames

RightToLeftChaining

Chained accesses are invoked from right to left

RightToLeftChaining

Chained accesses are invoked from right to left

SelfNoExpression

The name self is not an expression

StringLiteralNoObject

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

StringPlusStringifiesExpression

String concatenation stringifies non-String operand expressions

ThisAssignable

One can assign to this

ThisAssignable

One can assign to this

ThisCanBeNull

this can be null

ThisExistsInStaticMethod

this is a local variable, also in static methods

ThisNoExpression

The name this is not an expression

VariablesHoldExpressions

= stores an expression in a variable

VariablesHoldExpressions

= stores an expression: it stores a reference to the expression in a variable

VariablesHoldObjects

A variable of a reference type contains a whole object

VariablesHoldObjects

A variable contains a whole object

Programming Language

Notional Machine

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