Which of the following is the operator used to determine whether an object?

Question

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Which of the following operators can you use to test if an object has a specific type?
What object oriented programming characteristic allows you to create a class that is a specialized version of another class?
What does instance of mean in Java?
What is the return type of the instance of operator?

The

class C {
  #x;
  static isC(obj) {
    try {
      obj.#x;
      return true;
    } catch {
      return false;
    }
  }
}

7 operator returns

class C {
  #x;
  static isC(obj) {
    try {
      obj.#x;
      return true;
    } catch {
      return false;
    }
  }
}

8 if the specified property is in the specified object or its prototype chain.

prop in object
#prop in object

class C {
  #x;
  static isC(obj) {
    try {
      obj.#x;
      return true;
    } catch {
      return false;
    }
  }
}

9

A string or symbol representing a property name (non-symbols will be ). Can also be a private property identifier.

class C {
  #x;
  static isC(obj) {
    return #x in obj;
  }
}

0

Object to check if it (or its prototype chain) contains the property with specified name (

class C {
  #x;
  static isC(obj) {
    try {
      obj.#x;
      return true;
    } catch {
      return false;
    }
  }
}

9).

class C {
  #x;
  static isC(obj) {
    return #x in obj;
  }
}

2

Thrown if

class C {
  #x;
  static isC(obj) {
    return #x in obj;
  }
}

0 is not an object (i.e. a primitive).

The

class C {
  #x;
  static isC(obj) {
    try {
      obj.#x;
      return true;
    } catch {
      return false;
    }
  }
}

7 operator tests if a string or symbol property is present in an object or its prototype chain. If you want to check for only non-inherited properties, use

class C {
  #x;
  static isC(obj) {
    return #x in obj;
  }
}

5 instead.

A property may be present in an object but have value

class C {
  #x;
  static isC(obj) {
    return #x in obj;
  }
}

6. Therefore,

class C {
  #x;
  static isC(obj) {
    return #x in obj;
  }
}

7 is not the same as

class C {
  #x;
  static isC(obj) {
    return #x in obj;
  }
}

8. To make

class C {
  #x;
  static isC(obj) {
    try {
      obj.#x;
      return true;
    } catch {
      return false;
    }
  }
}

7 return

class C {
  foo() {
    #x in this;
  }
}

new C().foo(); // SyntaxError: Private field '#x' must be declared in an enclosing class

0 after a property is added, use the

class C {
  foo() {
    #x in this;
  }
}

new C().foo(); // SyntaxError: Private field '#x' must be declared in an enclosing class

1 operator instead of setting that property's value to

class C {
  #x;
  static isC(obj) {
    return #x in obj;
  }
}

6.

You can also use the

class C {
  #x;
  static isC(obj) {
    try {
      obj.#x;
      return true;
    } catch {
      return false;
    }
  }
}

7 operator to check whether a particular private class field or method has been defined in an object. The operator returns

class C {
  #x;
  static isC(obj) {
    try {
      obj.#x;
      return true;
    } catch {
      return false;
    }
  }
}

8 if the property is defined, and

class C {
  foo() {
    #x in this;
  }
}

new C().foo(); // SyntaxError: Private field '#x' must be declared in an enclosing class

0 otherwise. This is known as a branded check, because it returns

class C {
  #x;
  static isC(obj) {
    try {
      obj.#x;
      return true;
    } catch {
      return false;
    }
  }
}

8 if and only if the object was created with that class constructor, after which you can safely access other private properties as well.

This is a special syntax — the left-hand side of the

class C {
  #x;
  static isC(obj) {
    try {
      obj.#x;
      return true;
    } catch {
      return false;
    }
  }
}

7 operator is a property identifier instead of an expression, but unquoted (because otherwise it's a string property, not a private property).

Because accessing private properties on objects unrelated to the current class throws a

class C {
  #x;
  static isC(obj) {
    return #x in obj;
  }
}

2 instead of returning

class C {
  #x;
  static isC(obj) {
    return #x in obj;
  }
}

6, this syntax allows you to shorten:

class C {
  #x;
  static isC(obj) {
    try {
      obj.#x;
      return true;
    } catch {
      return false;
    }
  }
}

To:

class C {
  #x;
  static isC(obj) {
    return #x in obj;
  }
}

It also generally avoids the need for dealing with error handling just to access a private property that may be nonexistent.

However, the

class C {
  #x;
  static isC(obj) {
    try {
      obj.#x;
      return true;
    } catch {
      return false;
    }
  }
}

7 operator still requires the private property to be declared beforehand in the enclosing class — otherwise, it would throw a

// Arrays
const trees = ["redwood", "bay", "cedar", "oak", "maple"];
0 in trees; // returns true
3 in trees; // returns true
6 in trees; // returns false
"bay" in trees; // returns false (you must specify the index number, not the value at that index)
"length" in trees; // returns true (length is an Array property)
Symbol.iterator in trees; // returns true

// Predefined objects
"PI" in Math; // returns true

// Custom objects
const mycar = { make: "Honda", model: "Accord", year: 1998 };
"make" in mycar; // returns true
"model" in mycar; // returns true

1 ("Private field '#x' must be declared in an enclosing class"), the same one as when you try to access an undeclared private property.

class C {
  foo() {
    #x in this;
  }
}

new C().foo(); // SyntaxError: Private field '#x' must be declared in an enclosing class

The following examples show some uses of the

class C {
  #x;
  static isC(obj) {
    try {
      obj.#x;
      return true;
    } catch {
      return false;
    }
  }
}

7 operator.

// Arrays
const trees = ["redwood", "bay", "cedar", "oak", "maple"];
0 in trees; // returns true
3 in trees; // returns true
6 in trees; // returns false
"bay" in trees; // returns false (you must specify the index number, not the value at that index)
"length" in trees; // returns true (length is an Array property)
Symbol.iterator in trees; // returns true

// Predefined objects
"PI" in Math; // returns true

// Custom objects
const mycar = { make: "Honda", model: "Accord", year: 1998 };
"make" in mycar; // returns true
"model" in mycar; // returns true

You must specify an object on the right side of the

class C {
  #x;
  static isC(obj) {
    try {
      obj.#x;
      return true;
    } catch {
      return false;
    }
  }
}

7 operator. For example, you can specify a string created with the

// Arrays
const trees = ["redwood", "bay", "cedar", "oak", "maple"];
0 in trees; // returns true
3 in trees; // returns true
6 in trees; // returns false
"bay" in trees; // returns false (you must specify the index number, not the value at that index)
"length" in trees; // returns true (length is an Array property)
Symbol.iterator in trees; // returns true

// Predefined objects
"PI" in Math; // returns true

// Custom objects
const mycar = { make: "Honda", model: "Accord", year: 1998 };
"make" in mycar; // returns true
"model" in mycar; // returns true

4 constructor, but you cannot specify a string literal.

const color1 = new String("green");
"length" in color1; // returns true

const color2 = "coral";
// generates an error (color2 is not a String object)
"length" in color2;

If you delete a property with the

class C {
  foo() {
    #x in this;
  }
}

new C().foo(); // SyntaxError: Private field '#x' must be declared in an enclosing class

1 operator, the

class C {
  #x;
  static isC(obj) {
    try {
      obj.#x;
      return true;
    } catch {
      return false;
    }
  }
}

7 operator returns

class C {
  foo() {
    #x in this;
  }
}

new C().foo(); // SyntaxError: Private field '#x' must be declared in an enclosing class

0 for that property.

const mycar = { make: "Honda", model: "Accord", year: 1998 };
delete mycar.make;
"make" in mycar; // returns false

const trees = ["redwood", "bay", "cedar", "oak", "maple"];
delete trees[3];
3 in trees; // returns false

If you set a property to

class C {
  #x;
  static isC(obj) {
    return #x in obj;
  }
}

6 but do not delete it, the

class C {
  #x;
  static isC(obj) {
    try {
      obj.#x;
      return true;
    } catch {
      return false;
    }
  }
}

7 operator returns true for that property.

const mycar = { make: "Honda", model: "Accord", year: 1998 };
mycar.make = undefined;
"make" in mycar; // returns true

const trees = ["redwood", "bay", "cedar", "oak", "maple"];
trees[3] = undefined;
3 in trees; // returns true

The

class C {
  #x;
  static isC(obj) {
    try {
      obj.#x;
      return true;
    } catch {
      return false;
    }
  }
}

7 operator will return

class C {
  foo() {
    #x in this;
  }
}

new C().foo(); // SyntaxError: Private field '#x' must be declared in an enclosing class

0 for , even if accessing it directly returns

class C {
  #x;
  static isC(obj) {
    return #x in obj;
  }
}

6.

const empties = new Array(3);
empties[2]; // returns undefined
2 in empties; // returns false

To avoid this, make sure a new array is always filled with non-empty values or not write to indexes past the end of array.

class C {
  #x;
  static isC(obj) {
    try {
      obj.#x;
      return true;
    } catch {
      return false;
    }
  }
}

0

The

class C {
  #x;
  static isC(obj) {
    try {
      obj.#x;
      return true;
    } catch {
      return false;
    }
  }
}

7 operator returns

class C {
  #x;
  static isC(obj) {
    try {
      obj.#x;
      return true;
    } catch {
      return false;
    }
  }
}

8 for properties in the prototype chain. This may be undesirable if you are using objects to store arbitrary key-value pairs.

class C {
  #x;
  static isC(obj) {
    try {
      obj.#x;
      return true;
    } catch {
      return false;
    }
  }
}

1

You can use

class C {
  #x;
  static isC(obj) {
    return #x in obj;
  }
}

5 to check if the object has the key.

class C {
  #x;
  static isC(obj) {
    try {
      obj.#x;
      return true;
    } catch {
      return false;
    }
  }
}

2

Alternatively, you should consider using a or a

const color1 = new String("green");
"length" in color1; // returns true

const color2 = "coral";
// generates an error (color2 is not a String object)
"length" in color2;

6 for storing

const color1 = new String("green");
"length" in color1; // returns true

const color2 = "coral";
// generates an error (color2 is not a String object)
"length" in color2;

7, to avoid other bugs.

class C {
  #x;
  static isC(obj) {
    try {
      obj.#x;
      return true;
    } catch {
      return false;
    }
  }
}

3

The code fragment below demonstrates a static function that tells if an object was created with the

const color1 = new String("green");
"length" in color1; // returns true

const color2 = "coral";
// generates an error (color2 is not a String object)
"length" in color2;

8 constructor and therefore can perform other methods safely.

class C {
  #x;
  static isC(obj) {
    try {
      obj.#x;
      return true;
    } catch {
      return false;
    }
  }
}

4

It helps to prevent the following case:

class C {
  #x;
  static isC(obj) {
    try {
      obj.#x;
      return true;
    } catch {
      return false;
    }
  }
}

5

Without the

class C {
  #x;
  static isC(obj) {
    try {
      obj.#x;
      return true;
    } catch {
      return false;
    }
  }
}

7 operator, you would have to use a

const mycar = { make: "Honda", model: "Accord", year: 1998 };
delete mycar.make;
"make" in mycar; // returns false

const trees = ["redwood", "bay", "cedar", "oak", "maple"];
delete trees[3];
3 in trees; // returns false

0 block to check if the object has the private property.

You can also implement this as a

const mycar = { make: "Honda", model: "Accord", year: 1998 };
delete mycar.make;
"make" in mycar; // returns false

const trees = ["redwood", "bay", "cedar", "oak", "maple"];
delete trees[3];
3 in trees; // returns false

1 method of the class, so that you can use the

const mycar = { make: "Honda", model: "Accord", year: 1998 };
delete mycar.make;
"make" in mycar; // returns false

const trees = ["redwood", "bay", "cedar", "oak", "maple"];
delete trees[3];
3 in trees; // returns false

2 operator to perform the same check (which, by default, only checks for the existence of

const mycar = { make: "Honda", model: "Accord", year: 1998 };
delete mycar.make;
"make" in mycar; // returns false

const trees = ["redwood", "bay", "cedar", "oak", "maple"];
delete trees[3];
3 in trees; // returns false

3 in the object's prototype chain).

Which of the following operators can you use to test if an object has a specific type?

The instanceof operator compares an object to a specified type. You can use it to test if an object is an instance of a class, an instance of a subclass, or an instance of a class that implements a particular interface.

What object oriented programming characteristic allows you to create a class that is a specialized version of another class?

Inheritance allows programmers to create classes that are built upon existing classes, to specify a new implementation while maintaining the same behaviors (realizing an interface), to reuse code and to independently extend original software via public classes and interfaces.

What does instance of mean in Java?

Definition and Usage The instanceof keyword checks whether an object is an instance of a specific class or an interface. The instanceof keyword compares the instance with type. The return value is either true or false .

What is the return type of the instance of operator?

The instanceof in java is also known as type comparison operator because it compares the instance with type. It returns either true or false. If we apply the instanceof operator with any variable that has null value, it returns false.

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