Java编程思想第四版第三章练习

练习1：使用“简短的”和 正常的打印语句来编写一个程序

import java.util.Date;import net.mindview.util.Print.*;/*要想使用这个类库，必须从www.MindView.net或其镜像之一下载本书的代码包，然后解压代码目录树，并在你的计算机的CLASSPATH环境变量中添加该代码目录树的根目录。（你最终会获得有关类路径的完整介绍，但是你也应该尽早习惯它带来的麻烦。唉，它是你在使用Java时最常见的问题之一。）*/public class Exercise3_1 {  public static void main(String[] args) {     Print(new Date());    System.out.println(new Date());}}

练习2：创建一个包含一个float域的类。并用这个类来展示别名机制。

public class Exercise3_2 {    public static void main(String[] args) {        Integral integral1 = new Integral();        Integral integral2 = new Integral();        integral1.f=9f;        integral2.f=47f;        System.out.println("1:integral1.f="+integral1.f+",integral2.f="+integral2.f);        integral1=integral2;        System.out.println("2:integral1.f="+integral1.f+",integral2.f="+integral2.f);        integral1.f=27f;        System.out.println("3:integral1.f="+integral1.f+",integral2.f="+integral2.f);    }}class Integral{    float f;}/* Output 1:integral1.f=9.0,integral2.f=47.0 2:integral1.f=47.0,integral2.f=47.0 3:integral1.f=27.0,integral2.f=27.0 */

练习3：创建一个包含一个float域的类。并用这个类来展示方法调用时的别名机制。

public class Exercise3_3 {  static void f(Integral y) {      y.f=1.0f;  }  public static void main(String[] args) {    Integral x = new Integral();    x.f = 2.0f;    System.out.println("1:x.f="+x.f);    f(x);    System.out.println("2:x.f="+x.f);}}/* Output 1:x.f=2.0 2:x.f=1.0*/    

练习4 ：编写一个计算速度的程序，它所使用的距离和时间都是常量。

public class Exercise3_4 {    public static void main(String[] args) {        float distance = 100;        float time=20;        float velocity =distance/time;        System.out.println("Velocity = "+velocity+" m/s");    }}

练习5：创建一个名为dog的类，它包含两个string域：name和says。在main()方法中，创建两个Dogs对象，一个名为spot（它的叫声为“ Ruff!”），另一个名为scruffy（它的叫声为”Wuff!”）。然后显示它们的名字和叫声。

public class Exercise3_5 {  public static void main(String[] args) {    Dog dog1 = new Dog();    dog1.name = "spot";    dog1.says = "Ruff!";    System.out.println(dog1.name+" says "+dog1.says);    Dog dog2 = new Dog();    dog2.name = "scruffy";    dog2.says = "Wurf!";    System.out.println(dog2.name+" says "+dog2.says);}}class Dog{    String name;    String  says;}

练习6：在练习（5）的基础上，创建一个新的Dog索引，并对其赋值为spot对象。测试用==和equals（）方法来比较所有引用的结果

public class Exercise3_6 {    static void compare(Dog dog1,Dog dog2) {        System.out.println("== on top references: "+(dog1==dog2));        System.out.println(".equals() on top references: "+dog1.equals(dog2));        System.out.println("== on name: "+(dog1.name==dog2.name));        System.out.println(".equals() on name: "+dog1.name.equals(dog2.name));        System.out.println("== on Says: "+(dog1.says==dog2.says));        System.out.println(".equals() on Says: "+dog1.says.equals(dog2.says));    }     public static void main(String[] args) {            Dog dog1 = new Dog();            dog1.name = "spot";            dog1.says = "Ruff!";            Dog dog2 = new Dog();            dog2.name = "scruffy";            dog2.says = "Wurf!";            Dog dog3 = dog1;            System.out.println("Compareing dog1 and dog2 objects");            compare(dog1, dog2);            System.out.println("Compareing dog1 and dog3 objects");            compare(dog1, dog3);            System.out.println("Compareing dog2 and dog3 objects");            compare(dog2, dog3);        }        }        class Dog{            String name;            String says;        }

练习7：编写一个程序，模拟扔硬币的结果。

public class Exercise3_7 {   public static void main(String[] args) {    Random random = new Random(47);    boolean flip = random.nextBoolean();    System.out.println(flip==true?"Head":"Tail");}}

练习8：展示用十六进制和八进制计数法来操作long值，用Long.toBinaryString()来显示结果。

public class Exercise3_8 { public static void main(String[] args) {    long l1 = 0x2f;    System.out.println("l1: "+Long.toBinaryString(l1));    long l2 = 0X2F;    System.out.println("l2: "+Long.toBinaryString(l2));    long l3 = 0177;    System.out.println("l3: "+Long.toBinaryString(l3));}}/* Outputl1: 101111l2: 101111l3: 1111111*/

练习9：分别显示用float和double指数记数法所能表示的最大和最小的数字。

public class Exercise3_9 {  public static void main(String[] args) {      System.out.println("Float.MAX_VALUE = "+Float.MAX_VALUE);      System.out.println("Float.MIN_VALUE = "+Float.MIN_VALUE);    System.out.println("Double.MAX_VALUE = "+Double.MAX_VALUE);    System.out.println("Double.MIN_VALUE = "+Double.MIN_VALUE);}}/* Output Float.MAX_VALUE = 3.4028235E38Float.MIN_VALUE = 1.4E-45Double.MAX_VALUE = 1.7976931348623157E308Double.MIN_VALUE = 4.9E-324 */

练习10： 编写一个具有两个常量值的程序,一个具有交替的二进制位1和0,其中最低有效位为0,另一个也具有交替的二进制位1和0,但其最低有效位为1(提示:使用十六进制常量来表示最简单的方法).取两个值,用按位操作符以所有可能方式结合运算它们,然后anteger.toBinaryString()显示

public class Exercise3_10 {  public static void main(String[] args) {    int i1 = 0Xaaaaaaaa;    int i2 = 0x55555555;    System.out.println("i1 = "+Integer.toBinaryString(i1));    System.out.println("i2 = "+Integer.toBinaryString(i2));    System.out.println("~i1 =  "+Long.toBinaryString(~i1));    System.out.println("~i2 = "+Long.toBinaryString(~i2));    System.out.println("i1&i1 =  "+Long.toBinaryString(i1&i1));    System.out.println("i1|i1 =  "+Long.toBinaryString(i1|i1));    System.out.println("i1^i1 =  "+Long.toBinaryString(i1^i1));    System.out.println("i1&i2 =  "+Long.toBinaryString(i1&i2));    System.out.println("i1|i2 =  "+Long.toBinaryString(i1|i2));    System.out.println("i1^i2 =  "+Long.toBinaryString(i1^i2));}}

练习11：以一个最高有效位为1的二进制数字开始（提示：使用十六进制常量），用有符号右移操作符对其进行右移，直至所有的二进制位都被移除为止，每移一位都要使用Integer.toBinaryString()显示结果

public class Exercise3_11 {public static void main(String[] args) {    int i = 0X80808080;    System.out.println(Integer.toBinaryString(i));    for (int j = 0; j < 32; j++) {        i>>=1;    System.out.println(Integer.toBinaryString(i));    }}}

练习12：以一个所有位为1的二进制数字开始，先左移它，然后用无符号右移操作符对其右移，直至所有的二进制位都被移除为止，每移一位都要使用Integer.toBinaryString()显示结果。

public class Exercise3_12 { public static void main(String[] args) {   int i = -1<<1;   System.out.println(Integer.toBinaryString(i));   for (int j = 0; j < 32; j++) {       i>>>=1;   System.out.println(Integer.toBinaryString(i));}}}

练习13：编写一个方法，它以二进制形式显示char类型的值，使用多个不同的字符显示它。

public class Exercise3_13 {    static void f(char c) {        System.out.println(c+": "+Integer.toBinaryString(c));    }  public static void main(String[] args) {    f('A');}}

练习14 ：编写一个接收两个字符串参数的方法，用各种布尔值的比较关系来比较这两个字符串，然后把结果打印出来。做==和！=的同时，用equals()作测试。在main()里面用几个不同的字符串对象调用这个方法。

public class Exercise3_14 {     static void compare(String s1,String s2) {         System.out.println("s1 ="+s1+",s1 ="+s1);         p(s1+"=="+s2,s1==s2);         p(s1+"!="+s2,s1!=s2);         p(s1+".equals("+s2+")",s1.equals(s2));     }     static void p(String s,boolean b) {         System.out.println(s+" "+b);     }  public static void main(String[] args) {    compare("hello", "hello");    String s = new String("hello");    compare("hello", s);    compare("hello", "World");}}