第二周 - Elementary Programming

2.9 Are the following statements correct? If so,show the output.

public class Demo {public static void main(String[] args) {System.out.println("25/4 is " + 25 / 4);System.out.println("25/4.0 is " + 25 / 4.0);System.out.println("3*2/4 is " + 3 * 2 / 4);System.out.println("3.0*2/4 is " + 3.0 * 2 / 4);}}

2.18 Show the following output.

public class Demo {public static void main(String[] args) {float f = 12.5F;int i = (int) f;System.out.println("f is " + f);System.out.println("i is " + i);}

2.20 Which of the following are correct literals for characters?

public class Demo {public static void main(String[] args) {float f = 12.5F;int i = (int) f;System.out.println('1');System.out.println('\u3fFa');System.out.println('\b');}}

 The '\u345dE' and \t is wrong.

2.21 How do you display characters \ and "?

public class Demo {public static void main(String[] args) {System.out.println("\\");System.out.println("\"");}}

2.22 Evaluate the following:

public class Demo {public static void main(String[] args) {int i = '1';int j = '1' + '2';int k = 'a';char c = 90;System.out.println("i=" + i + " j=" + j + " k=" + k + " c=" + c);}}

2.23 Can the following conversions involving casting be allowed? If so, find the converted result.

public class Demo {public static void main(String[] args) {char c = 'A';float f = 1000.34f;int i = (int) f;i = (int) c;System.out.println("i=" + i + " c=" + c + " f=" + f);}}

public class Demo {public static void main(String[] args) {double d = 1000.34;int i = (int) d;System.out.println("i=" + i + " d=" + d);}}

public class Demo {public static void main(String[] args) {int i = 97;char c = (char) i;System.out.println("i=" + i + " c=" + c);}}

2.24 Show the output of the following program:

public class Demo {public static void main(String[] args) {char x = 'a';char y = 'c';System.out.println(++x);System.out.println(y++);System.out.println(x - y);}}

2.25 Show the output of the following statements:

public class Demo {public static void main(String[] args) {System.out.println("1" + 1);System.out.println('1' + 1);System.out.println("1" + 1 + 1);System.out.println("1" + (1 + 1));System.out.println('1' + 1 + 1);}}

2.26 Evaluate the following expressions:

public class Demo {public static void main(String[] args) {System.out.println(1 + "welcome" + 1 + 1);System.out.println(1 + "welcome" + (1 + 1));System.out.println(1 + "welcome" + ('\u0001' + 1));System.out.println(1 + "welcome" + 'a' + 1);}}

2.6** Write a program that reads an integer between 0 and 100 and adds all the digits in the integer.For example,if an integer is 932,the sum of all its digits is 14.

import javax.swing.JOptionPane;public class Demo {public static void main(String[] args) {int sum=0,number;String input=JOptionPane.showInputDialog("Please input a number:");number=Integer.parseInt(input);while(number>0){sum=sum+(number%10);number/=10;}JOptionPane.showMessageDialog(null, "The digits is "+sum);}}

import java.util.Scanner;public class Demo {public static void main(String[] args) {int sum=0,number;//String input=JOptionPane.showInputDialog("Please input a number:");Scanner input=new Scanner(System.in);number=input.nextInt();while(number>0){sum=sum+(number%10);number/=10;}//JOptionPane.showMessageDialog(null, "The digits is "+sum);System.out.println("The digits is "+sum);}}

2.24 Give an airplane's acceleration a and take-off speed v,you can compute the minimum runway length needed for an airplane to take off using the following formula:

length=v*v/2a

write a program that prompts the user to enter v in m/s and the acceleration a in m/s*s,and display the minimum runway length.

import javax.swing.JOptionPane;public class Demo {public static void main(String[] args) {String v, a;double v0, a0, length;v = JOptionPane.showInputDialog("Please input the speed v:");a = JOptionPane.showInputDialog("Please input the acceleration a:");v0 = Double.parseDouble(v);a0 = Double.parseDouble(a);length = (v0 * v0) / (2 * a0);java.text.DecimalFormat df = new java.text.DecimalFormat("#.###");JOptionPane.showMessageDialog(null,"The minimum length is " + df.format(length) + "m.", "Result",JOptionPane.INFORMATION_MESSAGE);}}

import java.util.Scanner;public class welcome {public static void main(String[] args) {double v0, a0, length;Scanner input = new Scanner(System.in);v0 = input.nextDouble();a0 = input.nextDouble();length = (v0 * v0) / (2 * a0);java.text.DecimalFormat df = new java.text.DecimalFormat("#.###");System.out.println("The minimum length is " + df.format(length) + "m.");}}