自用 | bb选择题 assgn1（chapter09 对象和类）

问题 1

Analyze the following code.

public class Test {int x;public Test(String t) {System.out.println("Test");}public static void main(String[] args) {Test test = new Test();System.out.println(test.x);}
}

A.The program has a compile error because x has not been initialized.

B.The program has a compile error because you cannot create an object from the class that defines the object.

C.The program has a compile error because Test does not have a default constructor.

D.The program has a compile error because System.out.println method cannot be invoked from the constructor.

问题2

The java.util.Date class is introduced in this section. Analyze the following code and choose the best answer:

Which of the following code in A or B, or both creates an object of the Date class:

public class Test {public Test() {new java.util.Date();}
}

public class Test {public Test() {java.util.Date date = new java.util.Date();}
}

A.A.

B.Neither

C.B.

问题 3

What code may be filled in the blank without causing syntax or runtime errors:

public class Test {java.util.Date date;public static void main(String[] args) {Test test = new Test();System.out.println(_________________);}
}

A.test.date

B.test.date.toString()

C.date.toString()

D.date

问题 4

What is the output of the following program?

import java.util.Date;
public class Test {public static void main(String[] args) {Date date = new Date(1234567);m1(date);System.out.print(date.getTime() + " ");m2(date);System.out.println(date.getTime());}public static void m1(Date date) {date = new Date(7654321);}public static void m2(Date date) {date.setTime(7654321);}
}

A.7654321 7654321

B.7654321 1234567

C.1234567 1234567

D.1234567 7654321

问题 5

What is the value of myCount.count displayed?

public class Test {public static void main(String[] args) {Count myCount = new Count();int times = 0;for (int i=0; i<100; i++)increment(myCount, times);System.out.println("myCount.count = " + myCount.count);System.out.println("times = "+ times);}public static void increment(Count c, int times) {c.count++;times++;}
}
class Count {int count;Count(int c) {count = c;}Count() {count = 1;}
}

A.101

B.99

C.98

D.100

问题 6

What is wrong in the following code?

class TempClass {int i;public void TempClass(int j) {int i = j;}
}
public class C {public static void main(String[] args) {TempClass temp = new TempClass(2);}
}

A.The program has a compilation error because TempClass does not have a default constructor.

B.The program compiles and runs fine.

C.The program has a compilation error because TempClass does not have a constructor with an int argument.

D.The program compiles fine, but it does not run because class C is not public.

问题 7

A constructor can access ___________.

A.A public instance variable

B.A private instance variable

C.A local variable defined in any method

D.A static variable

问题 8

A method that is associated with an individual object is called __________.

A.a class method

B.an object method

C.a static method

D.an instance method

问题 9

All local variables in a method have default values.

A.false

B.true

问题 10

An object is an instance of a __________.

A.class

B.program

C.data

D.method

问题 11

Analyze the following code.

public class Test {int x;public Test(String t) {System.out.println("Test");}public static void main(String[] args) {Test test = null;System.out.println(test.x);}
}

A.The program has a runtime NullPointerException because test is null while executing test.x.

B.The program has a compile error because Test does not have a default constructor.

C.The program has a compile error because x has not been initialized.

D.The program has a compile error because test is not initialized.

E.The program has a compile error because you cannot create an object from the class that defines the object.

问题 12

Analyze the following code:

class Test {private double i;public Test(double i) {this.t();this.i = i;}public Test() {System.out.println("Default constructor");this(1);}public void t() {System.out.println("Invoking t");}
}

A.this.t() may be replaced by t().

B.this(1) must be replaced by this(1.0).

C.this(1) must be called before System.out.println("Default constructor").

D.this.i may be replaced by i.

问题 13

Analyze the following code:

public class Test {public static void main(String[] args) {A a = new A();a.print();}
}
class A {String s;A(String s) {this.s = s;}void print() {System.out.println(s);}
}

A.The program compiles and runs fine and prints nothing.

B.The program has a compilation error because class A does not have a default constructor.

C.The program would compile and run if you change A a = new A() to A a = new A("5").

D.The program has a compilation error because class A is not a public class.

问题 14

Given the declaration Circle x = new Circle(), which of the following statement is most accurate？

A.x contains an int value.

B.You can assign an int value to x.

C.x contains a reference to a Circle object.

D.x contains an object of the Circle type.

问题 15

Which of the following statements are true?

A.At least one constructor must always be defined explicitly.

B.The default constructor is a no-arg constructor.

C.A default constructor is provided automatically if no constructors are explicitly declared in the class.

D.Every class has a default constructor.

问题 16

You can access a class variable using a syntax like objectName.classVariable or ClassName.classVariable.

A.false

B.true

问题 17

You use the _________ operator to access members of an object.

A..

B.*

C.()

D.%

问题 18

________ is invoked to create an object.

A.The main method

B.A method with the void return type

C.A constructor

D.A method with a return type

问题 19

__________ represents an entity in the real world that can be distinctly identified.

A.A method

B.A data field

C.A class

D.An object

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