U05
a
A characteristic of generic technique is ...... It adds stability to the code by making more of bugs detectable at compile time. It causes the code too complex. It decreases the code readability. None of the others.
Number
All of the numeric wrapper classes are subclasses of the abstract class ______. Double Class Integer Number None of the others.
java.lang.Number
All of the numeric wrapper classes in the java.lang package are subclasses of the abstract class ... java.lang.Integer java.lang.Number java.lang.Object java.lang.Wrapper None of the others
true, true, true
An instance of the java.util.Scanner class can read data from the keyboard (1), a file (2), a string of characters (3). (1) is ......., (2) is ......., and (3) is ........... true, true, false true, false, true true, true, true true, false, false None of the others
none
Given a string constructed by calling s = new String( "xyzzy" ), which of the calls modifies the string? (Choose one.) s.append( "aaa" ); s.trim(); s.substring(3); s.replace('z', 'a'); s.concat(s); None of the others.
1.0
If we use Math.random() method to random a number, which of the following numbers will never be appeared? 0.2 0.1 1.0 0.4
SortedSet
If we want to store a group of different elements in ascending order, the java.util.... class should be used. Vector ArrayList SortedSet HashMap HashSet
java.util.ArrayList
In Java Collection framework, which of the following pre-defined classes allow an element can be accessed through its index? java.util.ArrayList java.util.TreeMap java.util.TreeSet java.util.HashSet
java.lang.Comparable
In order to use the TreeSet class, the class that describes elements must implement the ... interface. java.lang.Comparing java.util.Comparable java.lang.Comparable java.util.treeset.Compare None of the others
java.lang.Comparable
In order to use the TreeSet class, the class that describes elements must implement the ______ interface. java.util.Compare java.collection.Comparator java.lang.Comparable java.tree.set.Element None of the others.
b
In which situation are generic collections used? ) The collection contains elements which belong to some classes. The collection contains homogenous elements. The collection contains elements which belong to exactly two classes. None of the others
a
One of the difference about Lists and Sets: A list can contain duplicate items but a set can not. Lists can add primitive type only and Sets can add object references. The number of items that can be added to Lists is limited; there is no such limitation for Sets. There is no difference.
none
String S= "Hello"; String S2= new String("Hello"); The String class describes an immutable chain of Unicode characters. Select a statement that causes an error. S= S.toUpperCase(); S=S + " Chan"; boolean b = (S==S2); None of the others.
none
String S= "Hello"; String S2= new String("Java Program"); The String class describes an immutable chain of Unicode characters. Select a statement that causes an error. None of the others. S="Innovation"; S2=S.toUpperCase(); S+=S2; All of these assignment statement.
1, 17
Study the following Java statements: String S= "William, Bill is ill."; int index1= S.indexOf("ill"); int index2= S.lastIndexOf("ill"); The value of index1 is ..... and index2 is ...... 1, 17 17, 1 2, 18 18, 2 None of the others.
a
Study the following Java statements: String s1= "Hello"; String s2= "Hello"; String s3= "Hello"; There is only one string is stored in memory of the program. There is two strings are stored in memory of the program. There is three strings are stored in memory of the program. None of the others.
Unboxing, boxing
Study the following code was implemented in the Hello class: static void print(Integer obj){ System.out.println(obj); } And it is used as: Integer obj= new Integer(5); int n= obj; //(1) Hello.print( n ); //(2) A ..... operation is carried out at the code line (1) A ..... operation is carried out at the code line (2) Boxing, unboxing Wrapping, un-wrapping Unboxing, boxing None of the others.
e
Suppose prim is an int and wrapped is an Integer. Which of the following are legal Java statements? (Choose one.) prim = wrapped; wrapped = prim; prim = new Integer( 9 ); wrapped = 9; All the others.
java.util.ArrayList list;
Suppose that a homogenous collection of objects, that belong the same type, are managed. Which of the following delarations is the best choice? java.util.Vector list; java.util.TreeSet list; java.util.ArrayList list; java.util.List list;
a
Suppose that obj1 and obj2 are objects and they belong to the same class. Study the semantics of following statements: (1) if (obj1==obj2) { } (2) if (obj1.equals( obj2 )) { } (1) and (2) are different. (1) and (2) are the same. (1) uses deep comparison (2) uses swallow comparison
a swallow comparison
Suppose that obj1 and obj2 are reference variables. The expression obj1==obj2 will execute ...... a deep comparison. a swallow comparison. a swallow copy. a deep copy.
StringBuilder
Suppose that: - Your application has to read and write a string a lot of times. -Your application does not need to have multi threaded supports. - Performance is important. Which of the following classes will you choose to deal with string data type to achieve the above requirements? StringBuffer String StringPrinter StringBuilder
none
The Java Collection framework is implemented in the ...package. None of the others. java.util.framework java.util.collection java.collection java.lang
java.util
The Java Collection framework is implemented in the ______ package. java.collection java.framework java.colectionframework java.lang java.util
Object
The _____ class is the ultimate ancestor of all Java classes. Object Class Concept AbstractObject None of the others.
Collection
The top interface of the Java Collection Framework is....... List Map Set Collection All of the others.
Iterator
To traverse elements in a set, one after one element, the java.util........interface must be use. List Set Iterator Map
a
When invoking Math.random(), which of the following options might be the result? The result is less than 1.0 The result is greater than 1.0 The result is equal 1.0 The result is from 1 to 100
TreeSet
Which of the following Java lists that allows data is stored in sorted order, and also, no duplicate data is allowed? ArrayList Vector TreeSet LinkedList
none
Which of the following classes is the ultimate ancestor of all Java classes? Class Concept Thing None of the others
Array
Which of the following collection cannot be used with Iterator class to traverse through elements? ArrayList TreeSet Array HashMap
a
Which of the following options is correct? Values stored in TreeSet are not allowed duplication Values stored in ArrayList are automatically sorted Values stored in Vector can be assessed through key-value pair. None of the others
none
Which of the following options is not a method of java.lang.Math Class? None of the others pow() floor() ceil() max()
nextValue()
Which of the following options is not a method of the Scanner class? nextValue() next() nextInt() nextDouble()
b
Which of the following statements is true about Object class? By default, the clone() method performs deep copy of an object By default, the equals() method simply performs the == operator By default, the toString() method returns the name of the class By default, the toString() method returns the address of the class
a
Which one statement is true about the following code fragment? (choose 1) 1. import java.lang.Math; 2. Math myMath = new Math(); 3. System.out.println("cosine of 0.123 = " + myMath.cos( 0.123 ) ); Compilation fails at line 2. Compilation fails at line 3. Compilation succeeds, although the import on line 1 is not necessary. During execution, an exception is thrown at line 3. Compilation succeeds. The import on line 1 is necessary. During execution, an exception is thrown at line 3. Compilation succeeds and no exception is thrown during execution.
c
Which one statement is true about the following code? 1. String s1 = "abc" + "def"; 2. String s2 = new String(s1); 3. if (s1 == s2) 4. System.out.println("== succeeded"); 5. if (s1.equals(s2)) 6. System.out.println(".equals() succeeded"); Lines 4 and 6 both execute. Line 4 executes and line 6 does not. Line 6 executes and line 4 does not. Neither line 4 nor line 6 executes.
Collections.shuffle()
You are required to build a Java application. Your application uses Vector to store data. Each time elements, taken from the vector, should be displayed to users in a random order. Which of the following methods can be used to achieve the above task? Collections.shuffle() Collections.random() Collections.radomElement() Collections.mix()
a
You are required to validate an email string taken from users. A valid email form should be [email protected]. Select a correct pattern that can be used to validate email input: "^\w+@\w+[.]\w+$" "^\w+@\w+.\w+$" "^\w?@\w+[.]\w+$"
