(100 total points)

Directions: Give brief but precise answers to the following questions.

• Name and describe the three types of Java loops. (5 pts)

do loop - do { statement(s) } while ( booleanExpression );

while loop - while ( booleanExpression ) { statement(s) }

for loop - for ( initStatement ; testExpression ; iterationExpression ) { statement(s) };

• Write a Java statement to declare an array called values of ten integers. (5 pts)

int[] values = new int[10];

• Write a Java statement to initialize each element of the above array to one more than its subscript value. (5 pts)

for (int i = 0; i < 10; ++i) { values[i] = i + 1; }

• Write a Java statement to declare an array called labels of two Label widgets and Java statements to initialize the two elements to Labels of "one" and "two". (5 pts)

Label[] labels = new Label[2];

labels[0] = new Label("one");

labels[1] = new Label("two");

• Describe the concept of Java heterogeneous arrays. (5 pts)

Java arrays with object elements may contain elements of any of the derived classes of the declared array element type. Normally, arrays are homogeneous and may have all elements of the same declared type.

• Describe the difference between selection and insertion sorts. (5 pts)

A selection sort selects the largest (or smallest) element from the remained unsorted portion of the list, placing it in its proper position via an exchange with the element currently in the position. An insertion sort inserts the next unsorted element into the already sorted portion of the list by moving sorted elements over one from the right until the correct position is found.

• Describe how the Vector class extends Java arrays. (5 pts)

They are dynamic (their size can be modified at any time), there is only one choice for the element type (always contain Object type), and comes with an extensive suite of powerful methods for manipulating the underlying array and its elements.

• Describe what it means that Java strings are immutable. (5 pts)

Once a String instance has been created, it cannot be changed. The string reference variable can only be assigned a new string.

• Write a Java statement to set the String variable compares to "less than", "equal to" , or "greater than" based on whether the value of the String first is less than, equal to, or greater than the value of the String second. (5 pts)

if (first.compareTo(second) < 1) { compares = "less than"; }

else if (first.compareTo(second) == 0) { compares = "equal to"; }

else { compares = "greater than"; }

• Write a Java "debug" statement to output the length of the array called message. (5 pts)

System.out.println(message.length);

• Write two Java statements to create a PrintStream called ps for the file "file.out" (use the variable fos) ignoring exception handling for this question. (5 pts)

FileOutputStream fos = new FileOutputStream("file.out");

PrintStream ps = new PrintStream(fos);

• Now write Java statements to output the value of a String called name, an int called age, a boolean called married which can be read back later. (Remember IOException) (5 pts)

try {

ps.print(name.length()); ps.print(","); ps.print(name); ps.print(",");

ps.print(age); ps.print(",")

ps.print(married); ps.println();

}

catch (IOException ioe) {

System.err.println(ioe);

}

• Describe error propagation in connection with the throws clause. (5 pts)

The throws clause says that the method which contains the clause may throw that exception and, if it does, the error will not be handled and should be passed to the block containing the method call. This passing of the error up the enclosing blocks will occur until a catch handler is found for that exception. If no handler is ever found, the Java run-time environment will eventually catch it.

• Describe the difference between the throw statement and the throws clause. (5 pts)

The throw statement causes an exception to occur; the throws clause says that execution of the method may cause the exception to occur.

• Describe the header method used with records in your text. (5 pts)

The header method writes a leading number which tells how many records follow.

• Contrast the three types of file I/O from IOConsoleAndFile.java (labelled Read/Write, ORead/OWrite, and TRead/TWrite on the buttons). (5 pts)

The Read/Write I/O reads/writes binary data from/to the file; the Oread/OWrite I/O reads/writes an objects data from/to the file in accordance with the readFrom and writeTo methods; and the TRead/TWrite reads/writes "ASCII-formatted" data converted to/from binary data.

• Contrast applets and windows applications in terms of security. (5 pts)

Applets normally are not allowed access to the client's file system, only the host's file system, whereas windows applications normally are allowed access to the local file system within what local permissions allow.

• Write a minimal Java windows application called DialogHello which simply displays a dialog containing the message "Hello, Dialog!". (15 pts)

import java.awt.*;

public class DialogHello extends Frame {

public DialogHello() {

Dialog d = new Dialog(this); d.add(new Label("Hello, Dialog!"));

d.setSize(100, 50); d.show();

}

public static void main(String[] args) { Frame f = new DialogHello(); f.show(); }

}

• (EXTRA) Describe the purpose of the File class. (+ 5 pts)

The File class contains a number of useful methods for finding information about files.

• (EXTRA) Describe the purpose of the finally clause. (+5 pts)

Finally clauses are generally used for cleanup purposes since statements in the try block following the one which caused the exception are never executed.