Misconceptions

AbstractClassMustImplementAbstractMethod

Java

DRAFT

An abstract class must implement all abstract methods defined in its superclass

Java

DRAFT

An abstract class cannot contain implemented methods

Java

DRAFT

All classes automatically get a no-argument constructor

Java

DRAFT

Any class can be an exception class

Java

DRAFT

Parenthesis are used to access an element in an array

Java

DRAFT

Arrays are created without the new keyword

Java

DRAFT

The number of brackets in an array type or an array initializer corresponds to the length of the array

Java

DRAFT

The type of a multi-dimensional array is written as T[] T[] T[]

Java

DRAFT

Elements of arrays are untyped

Java

DRAFT

Array initializers list the elements in square brackets

Java

DRAFT

An array cannot have a length of 0 elements

Java

DRAFT

The length of an array is part of its type

Java

DRAFT

Array rank and array length are the same thing

Java

DRAFT

The rank of an array is not part of its type

Java

DRAFT

Recursive computations do not necessarily need a base case

Java

DRAFT

The base case of a structural recursion consists of a recursive self-call

Java

DRAFT

Passing null to a wrapper class constructor creates an object representing the absence of a value

Java

DRAFT

One can invoke a method on primitive values

Java

DRAFT

One needs a variable to invoke a method

Java

DRAFT

A method invocation does not necessarily allocate a stack frame

Java

DRAFT

Stack frame of caller includes variables for callee's formal parameters

Java

DRAFT

Catch blocks always get executed

Java

DRAFT

Only the part of a catch block necessary to fix the cause of an exception is executed

Java

DRAFT

Chained methods are all called on the object at the beginning of the chain

Java

DRAFT

Expressions that consist of multiple parts have no type

Java

DRAFT

A concrete class needs to implement all abstract methods and override all concrete methods declared in its abstract superclasses

Java

DRAFT

A concrete class only needs to implement those abstract methods it inherits from abstract superclasses

ConcreteClassOnlyImplementDirectAbstract

Java

DRAFT

A concrete class only needs to implement abstract methods declared in its direct supertypes

ConcreteClassOnlyImplementInterfaceAbstract

Java

DRAFT

A concrete class only needs to implement those abstract methods it inherits from interfaces

Java

DRAFT

Formal constructor parameters are equivalent to instance variables

Java

DRAFT

One can write the constructor name, without new, to instantiate a class

Java

DRAFT

There is an elsif keyword for multi-way conditional statements

Java

DRAFT

The else branch of an if-else statement always executes

Java

DRAFT

Evaluating an expression means outputting its result

Java

DRAFT

Exception is the top-most exception class

Java

DRAFT

An expression that reads a variable also updates its value after the evaluation

Java

DRAFT

One has to evaluate an expression to determine its type

Java

DRAFT

An enhanced for loop iterates over the indices of an array or a collection

Java

DRAFT

For-each loops know how to traverse any recursive data structure

Java

DRAFT

One can assign to the variable of an enhanced for statement to store a value in the corresponding array or collection element

Java

DRAFT

The body of a for statement executes at most once

Java

DRAFT

The scope of variables declared in a for loop header extends beyond the loop

Java

DRAFT

A stack frame is the same as an instance of a class

Java

DRAFT

Every if statement requires an else

Java

DRAFT

Immutable classes need final constructor/method parameters

Java

DRAFT

Java implicitly produces implementations of any methods a class inherits from the interfaces it implements

Java

DRAFT

Dividing two integers can produce a rational number

Java

DRAFT

An interface can extend a class

Java

DRAFT

A literal is not an expression

Java

DRAFT

When passing a literal string as argument to a method, no quotes are needed

Java

DRAFT

Lifetime of variables declared in a loop body extends across all loop iterations

Java

DRAFT

For and while loops end when the condition becomes true

Java

DRAFT

Maps can store multiple values for a given key

Java

DRAFT

Map.put with an existing key does nothing

Java

DRAFT

Each object contains its own special fields for all of its methods

Java

DRAFT

A method declaration does not need to include a return type

Java

DRAFT

Methods can be defined outside a class

Java

DRAFT

A reference variable can point to multiple objects

Java

DRAFT

A variable can contain more than one value

Java

DRAFT

A multi-dimensional array is one single array object

Java

DRAFT

A class can have multiple superclasses

Java

DRAFT

To instantiate a generic type, one needs to specify type parameter names as well as types

Java

DRAFT

If objects are part of a containment hierarchy, their classes are nested, too

Java

DRAFT

Packages can contain other packages

Java

DRAFT

One cannot invoke methods on String literals

Java

DRAFT

If a variable is at least as big (bit-width) as a value, then no cast is needed to a assign the value to the variable

Java

DRAFT

\ is a normal character in char and String literals

Java

DRAFT

An object contains only the fields declared in its class

Java

DRAFT

Objects without instance variables can't exist

Java

DRAFT

Smaller types are never automatically converted into bigger ones without an explicit cast

Java

DRAFT

It is foirbidden to call other methods on the same object while inside its constructor

Java

DRAFT

Multi-dimensional arrays have a rectangular shape

Java

DRAFT

There are no local variables

Java

DRAFT

Subclasses inherit fields but not methods

Java

DRAFT

One cannot invoke toString() on a String

Java

DRAFT

NullPointerExceptions are detected at compile time

Java

DRAFT

Numeric types can be coerced to boolean

Java

DRAFT

Only the elements of the innermost array of a multi-dimensional array are accessible

Java

DRAFT

Only the creators of the JDK can create packages

Java

DRAFT

Out-of-bounds array elements are null

Java

DRAFT

Pre-increment in update part of for loop means increment before loop body

Java

DRAFT

Primitive values are heap objects

Java

DRAFT

Type parameters of generic types can be assigned primitive types

Java

DRAFT

The type of a primitive variable depends on its value

Java

DRAFT

println(...) starts a new line and then prints

Java

DRAFT

Private members of a superclass are accessible from a subclass

Java

DRAFT

A class where all fields are private is immutable

Java

DRAFT

A private field cannot be changed

Java

DRAFT

Rational fractions are literals

Java

DRAFT

Tail-recursive call sites have no continuation

Java

DRAFT

References can point into the stack

Java

DRAFT

Every reference type can be coerced to boolean

Java

DRAFT

One can cast between references and ints

ReferringToRecursiveStructureMakesRecursive

Java

DRAFT

A class referring to a recursive data structure is (indirectly) part of that recursion as well

Java

DRAFT

RuntimeExceptions are checked exceptions

SemanticEquivalenceImpliesSyntacticEquivalence

Java

DRAFT

Two pieces of code with the same observable behavior have to be implemented in the same way

Java

DRAFT

Setter methods are static

Java

DRAFT

String literals can be in single quotes

Java

DRAFT

A stack trace is the sequence of previously called methods

Java

DRAFT

A static method call is dispatched polymorphically at runtime based on the argument types

Java

DRAFT

The method to be called is determined by the static type

Java

DRAFT

One can know the length of a String object by accessing its length field

Java

DRAFT

The multiplication operator can repeat a String a number of times

Java

DRAFT

A variable of a subtype can reference an object of a supertype

Java

DRAFT

To call a method on a superclass, parentheses are needed after the keyword super

Java

DRAFT

super() can be called anywhere in the constructor of a subclass

Java

DRAFT

When instantiating an object of a subclass, an object of a superclass is also allocated

Java

DRAFT

A variable of a supertype cannot reference an object of a subtype

Java

DRAFT

The type of a numerical expression depends on the type expected by the surrounding context

Java

DRAFT

this is a special field in the object

Java

DRAFT

In a constructor, this is null

Java

DRAFT

Invoking toString() prints something

Java

DRAFT

If code could throw an exception, you must surround that code with a try/catch block

Java

DRAFT

Exceptions get thrown at the end of the try block

Java

DRAFT

Variables don't need to be declared

Java

DRAFT

The unqualified names of different classes must be different

Java

DRAFT

Variable declarations don't need a type

Java

DRAFT

If a class has a method that has a local variable, parameter, or return value with the class as its type, the class is a recursive type

Java

DRAFT

A method with void return type can't be recursive

Java

DRAFT

A method with void return type can return a value

Java

DRAFT

In integer numbers, decimal digits with value `0` take less storage than decimal digits with other values

JavaScript

DRAFT

Accessing a non existent property on an object produces an error

JavaScript

DRAFT

Even when an arrow function consists just of an expression, the return keyword must be explicitly written

JavaScript

DRAFT

Arrow functions also require the keyword 'function'

JavaScript

DRAFT

Parameters of a callback function may be written as parameters of the caller function

JavaScript

DRAFT

A single character is of type char

JavaScript

DRAFT

The conditional operator is not an expression

JavaScript

DRAFT

Declarations of constants do not need to be immediately initialized

JavaScript

DRAFT

The equality operator compares two objects' values

JavaScript

DRAFT

The equality operator '==' compares only the types of the operands

JavaScript

DRAFT

To use a function as a value, one needs to have parentheses after its name

JavaScript

DRAFT

It is possible to create multiple functions with the same name but with different signatures

JavaScript

DRAFT

Functions cannot be called in the expression in which they are defined

JavaScript

DRAFT

Every function definition requires an associated name

JavaScript

DRAFT

An identifier used to access a property with the bracket notation is treated as a string

JavaScript

DRAFT

An expression must be assigned to have a valid statement

JavaScript

DRAFT

Map modifies the elements of the array on which it operates in place

JavaScript

DRAFT

Square brackets cannot be used to access properties of an object

JavaScript

DRAFT

It is not allowed to chain function calls

JavaScript

DRAFT

There isn't a global object

JavaScript

DRAFT

Functions without return statements return no value at all

JavaScript

DRAFT

The values null and undefined are the same

JavaScript

DRAFT

Functions must be called with the same number of arguments as defined in their signature

JavaScript

DRAFT

Objects are passed by value

JavaScript

DRAFT

JavaScript is based on a class-based object model

JavaScript

DRAFT

Scheduling the execution of a function after 0 milliseconds with setTimeout is equivalent to a synchronous call

JavaScript

DRAFT

SetTimeout returns the value returned by the callback function

JavaScript

DRAFT

One can repeat a String by multiplying it with a number

JavaScript

DRAFT

The typeof operator applied on an array returns 'array'

JavaScript

DRAFT

The value null is of type 'null'

Python

DRAFT

There is no operator that repeats sequences

Python

DRAFT

The plus operator can concatenate strings and numbers

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