Lab Report

Caution

Must be original works, to prohibit any copying or plagiarism.

一、Experimental Purposes and Requirements

to learn Exception
to learn Text I/O.

二、 Experimental Contents

According to the the textbook，give a detailed reasong analysis of the every exercise in the Lab08(assignment_1)-chapter12 on platform of course.zucc.edu.cn.

For example:

What exception type does the following program throw?

public class Test {public static void main(String[] args) {System.out.println(1 / 0);}
}

A. ArithmeticException

B. ClassCastException

C. ArrayIndexOutOfBoundsException

D. StringIndexOutOfBoundsException

E. No exception

Sample answer

According to the content of “chapter 12.3 Exception type” and 12.2 Exception-Handling Overview,

The words which can best describe the reason is “XXXXXXXX”.

(NOTE, XXXXX MEANS THE ORIGINAL WORDS FROM THE TEXT.)

三、Please show your questions analysis, code and results.

1、Analyze the following code.

class Test {public static void main(String[] args) {    StringBuilder strBuf = new StringBuilder(4);   strBuf.append("ABCDE");    System.out.println("What's strBuf.charAt(5)? " + strBuf.charAt(5));  }
}

A.The program has a runtime error because because the buffer’s capacity is 4, but five characters “ABCDE” are appended into the buffer.

B.The program has a compilation error because you cannot specify initial capacity in the StringBuilder constructor.

C.The program compiles and runs fine.

D.The program has a runtime error because the length of the string in the buffer is 5 after “ABCDE” is appended into the buffer. Therefore, strBuf.charAt(5) is out of range.

According to the content of “10.11.2 The toString, capacity, length, setLength, and charAt Methods”, The words which can best describe the reason is

The charAt(index) method returns the character at a specific index in the string builder. The index is 0 based. The first character of a string builder is at index 0, the next at index 1, and so on. The index argument must be greater than or equal to 0, and less than the length of the string builder.

2、Analyze the following code.

class Test {public static void main(String[] args) {String s;System.out.println("s is " + s);}
}

A.The program has a compilation error because s is not initialized, but it is referenced in the println statement.

B.The program has a runtime error because s is null in the println statement.

C.The program has a runtime error because s is not initialized, but it is referenced in the println statement.

D.The program compiles and runs fine.

According to the content of “2.5 Variables”, The words which can best describe the reason is

For now, all you need to know is that a variable must be declared and initialized before it can be used.

3、Object-oriented programming allows you to derive new classes from existing classes. This is called ——.

A.generalization

B.abstraction

C.inheritance

D.encapsulation

According to the content of “chapter 12.3 Exception type” and 12.2 Exception-Handling Overview, The words which can best describe the reason is

Inheritance enables you to define a general class (i.e., a superclass) and later extend it to more specialized classes (i.e., subclasses).

4、Polymorphism means——

A.that a variable of supertype can refer to a subtype object

B.that a class can extend another class

C.that data fields should be declared private

D.that a class can contain another class

According to the content of “11.7 Polymorphism”, The words which can best describe the reason is

In simple terms, polymorphism means that a variable of a supertype can refer to a subtype object.

5、What is the output of the following code?

public class Test {public static void main(String[] args) {new Person().printPerson();new Student().printPerson();}
}class Student extends Person {private String getInfo() {return "Student";}
}class Person {private String getInfo() {return "Person";}public void printPerson() {System.out.println(getInfo());}
}

A.Person Student

B.Stduent Student

C.Person Person

D.Student Person

According to the content of “11.2 Superclasses and Subclasses”, The words which can best describe the reason is

TheCircle class inherits all accessible data fields and methods from the GeometricObject class. In addition, it has a new data field, radius, and its associated getter and setter methods. The Circle class also contains the getArea(), getPerimeter(), and getDiameter() methods for returning the area, perimeter, and diameter of the circle.

6、Which statements are most accurate regarding the following classes?

class A {private int i;protected int j;
}class B extends A {private int k;protected int m;// some methods omitted
}

A.In the class B, an instance method can only access i, j, k, m.

B.In the class B, an instance method can only access j, m.

C.In the class B, an instance method can only access k, m.

D.In the class B, an instance method can only access j, k, m.

According to the content of “11.2 Superclasses and Subclasses”, The words which can best describe the reason is

The Rectangle class inherits all accessible data fields and methods from the GeometricObject class.

At the same time, private variables in the parent class will not be called.

7、What is the output of running class Test?

public class Test {public static void main(String[] args) {new Circle9();}
}public abstract class GeometricObject {protected GeometricObject() {System.out.print("A");}protected GeometricObject(String color, boolean filled) {System.out.print("B");}
}public class Circle9 extends GeometricObject {/** No-arg constructor */public Circle9() {this(1.0);System.out.print("C");}/** Construct circle with a specified radius */public Circle9(double radius) {this(radius, "white", false);System.out.print("D");}/** Construct a circle with specified radius, filled, and color */public Circle9(double radius, String color, boolean filled) {super(color, filled);System.out.print("E");}
}

A.CBAE

B.ABCD

C.AEDC

D.BACD

E.BEDC

According to the content of “11.3 Using the super Keyword”, The words which can best describe the reason is

The keyword super refers to the superclass and can be used to invoke the superclass’s methods and constructors.

8、A subclass of a non-abstract class must be non-abstract.

A.false

B.true

C.101

D.99

According to the content of “13.2.2 Interesting Points about Abstract Classes”, The words which can best describe the reason is

A subclass can be abstract even if its superclass is concrete. For example, the Object class is concrete, but its subclasses, such as GeometricObject, may be abstract.

9、An abstract class can be extended.

A.true

B.false

According to the content of “13.2.2 Interesting Points about Abstract Classes”, The words which can best describe the reason is

An abstract method cannot be contained in a nonabstract class. If a subclass of an abstract superclass does not implement all the abstract methods, the subclass must be defined as abstract. In other words, in a nonabstract subclass extended from an abstract class, all the abstract methods must be implemented. Also note that abstract methods are nonstatic.

10、At least one method in an abstract class must be abstract.