CSci 2101: Review for Midterm I

What will be printed by the following program?

It would be helpful to keep track of values of i in a table.

public class ReviewOne {

	/**
	 * The program illustrates arrays for a midterm review
	 * Author: Elena Machkasova
	 * Date: 6/2/10
	 * What will be printed by the following program?
	 */
	public static void main(String[] args) {
		int [] data1 = {4, 7, 5, 8, 3};
		int [] data2 = {1, 6, 9, 7, 3};
		
		int [] result = new int[data1.length + data2.length];
		
		for (int i = 0; i < data1.length; ++i) {
			result[2*i] = data1[i];
			result[2*i + 1] = data2[i];
		}
		
		printIntArray();
	}
	
	/**
	 * 
	 * The method prints its argument <code>arr</code>
	 * element by element on one line, separated by commas,
	 * with [ before the first element and ] after the last one 
	 *
	 */
	public static void printIntArray(int [] arr) {
		System.out.print("[");
		for (int i = 0; i < arr.length; ++i) {
			System.out.print(arr[i]);
			if (i != arr.length - 1)
				System.out.print(", ");
		}
		System.out.println("]");
	}

}

What will be printed by the following program?

Draw memory picture for all the object variables involved.

import java.util.Stack;

public class Stacks {
    // What will be printed by the following program? 
	public static void main(String [] args){
		Stack<Integer> stack1 = new Stack<Integer>();
		Stack<Integer> stack2 = new Stack<Integer>();	
		Stack<Integer> stack3 = stack1;

		stack1.push(1);
		stack2.push(2);
		stack3.push(3);
		stack1.push(4);
		stack2.push(5);
		stack3.push(6);

		stack1.pop();
		stack2.pop();
		
		System.out.println("stack 1 = " + stack1);
		System.out.println("stack 2 = " + stack2);
		System.out.println("stack 3 = " + stack3);		
	}
}

Find and correct all mistakes in the program.

The method has to work as described in comments. Useless operations are considered a mistake. Type safety violations are considered a mistake, even if the program compiles and runs.

public class CorrectMistakes {
    // correct all mistakes in the following program:
    public static void main(String [] args) {
	int myarray = new int[10];

	for (int i = 1; i <= arr.size(); ++i) {
	    myarray[i] = i - 1;
	}

	printIntArray(myarray);
	replace(myarray);
	printIntArray(myarray);
    }

    /**
     * The method replaces all even elements n of the given array  
     * by n + 1.
     * The elements remain in the original order
     **/
    public static int [] replaceEvens(int [] arr) {
	for (j = 0; j < arr.length; ++j) {
	    if (arr[j] % 2 == 0) {
		myarray[i] = arr[j] + 1;
	    }
	}
	return arr;
    }

    /**
     * 
     * The method prints its argument arr
     * element by element on one line, separated by commas,
     * with [ before the first element and ] after the last one 
     *
     */
    public static void printIntArray(int [] arr) {
	System.out.print("[");
	for (int i = 0; i < arr.length; ++i) {
	    System.out.print(arr[i]);
	    if (i != arr.length - 1)
		System.out.print(", ");
	}
	System.out.println("]");
    }

}

Array problem

Write a program that finds and prints two largest elements in an array of ints.

Important: traverse the array only once!

Starting code for this problem:

public class TwoLargest {
    public static void main(String [] args) {
	// largest: 10, second largest: 9
	int [] items = {2, 5, 1, 7, 5, 3, 2, 9, 4, 3, 6, 10, 2, 8, 1};

	// your loop goes here
    }
}

Arrays, stacks, methods

Write and test a method that takes an array of strings and a stack of strings and returns true if the contents of the array is the same as that of the stack (the same strings in the same order) and false otherwise. The bottom of the stack corresponds to the first element of the array.
At the end of the method the stack must contain all of the initial elements in the same order as before the method.

CSci 2101 course web site.