java编程思想（第四版）练习题答案：一切都是对象

2.11 一切都是对象

练习1：创建一个类，它包含一个int域和一个char域，它们都没有被初始化，将它们的值值打印出来，以验证java执行了默认初始化。

// TIJ4 Chapter Object, Exericise 1, page 89 // object/PrimitiveTest.java // Create a class containing an int and a char that are not intitialized // and print their values to verify that Java performs default initialization.   public class PrimitiveTest {     static int i;     static char c;        public static void main(String[] args) {             System.out.println("int = " + i);        System.out.println("char = " + c);     } }

练习2：参照本章HelloDate.java这个例子，创建一个“Hello World”程序，该程序只要输出这句话即可。

// TIJ4 Chapter Object, Exericise 2, page 89 // object/HelloWorld.java // Following the HelloDate.java example in this chapter, create a "hello, world" // program that simply displays that statement.   public class HelloWorld {     public static void main(String[] args) {             System.out.println("Hello World!");     } }

练习3：找到含有AtypeName的代码段，将其改写成完整的程序，然后编译、运行。

// TIJ4 Chapter Object, Exericise 3, page 90 // object/ATNTest.java // Find the code fragments involving ATypeName and turn them into a program // that compiles and runs.   public class ATNTest {          public static void main(String[] args) {        class ATypeName {            int i;            double d;            boolean b;            void show() {               System.out.println(i);               System.out.println(d);               System.out.println(b);              }        }          ATypeName a = new ATypeName();        a.i = 3;        a.d = 2.71828;        a.b = false;             a.show();     } }

练习4：将DataOnly代码段，将其改写成完整的程序，然后编译、运行。

// object/DataOnlyTest.java // TIJ4 Chapter Object Exercise 4 page 90 // Turn the DataOnly code fragments into a program that compiles and runs   public class DataOnlyTest {     public static void main(String[] args) {        class DataOnly {            int i;            double d;            boolean b;            void show() {               System.out.println(i);               System.out.println(d);               System.out.println(b);              }        }          DataOnly data = new DataOnly();        data.i = 3;        data.d = 2.71828;        data.b = false;             data.show();     } }

练习5：修改前一个练习，将DataOnly中的数据在main()方法中赋值并打印出来。

// object/DOTest2.java // TIJ4 Chapter Object, Exercise 5, page 90 // Modify the previous exercise so that the values of the data in DataOnly are // assigned to and printed in main().   public class DOTest2 {          public static void main(String[] args) {        class DataOnly {            int i;            double d;            boolean b;            void show() {               System.out.println(i);               System.out.println(d);               System.out.println(b);              }        }          DataOnly data = new DataOnly();        data.i = 234;        data.d = 2.1234545;        data.b = true;              data.show();     } }

练习6：编写一个程序，让它含有本章所定义的storage()方法的代码段，并调用之。

// object/StorageTest.java // TIJ4 Chapter Object, Exercise 6, page 90 // Write a program that includes and calls the storage() method defined as a // code fragment in this chapter.   public class StorageTest {      public static void main(String[] args) {        class StoreStuff {            int storage(String s) {               return s.length() * 2;            }          }        StoreStuff x = new StoreStuff();        System.out.println(x.storage("hi"));          } }

练习7：将Incrementtable的代码段改成一个完整的可运行程序：

// object/ITest.java // TIJ4 Chapter Object, Exercise 7, page 90 // Turn the Incrementable code fragments into a working program.   class StaticTest {     static int i = 47; } class Incrementable {     static void increment() { StaticTest.i++; } } public class ITest {     public static void main(String[] args) {     System.out.println("StaticTest.i= " + StaticTest.i);     StaticTest st1 = new StaticTest();     StaticTest st2 = new StaticTest();     System.out.println("st1.i= " + st1.i);     System.out.println("st2.i= " + st2.i);     Incrementable sf = new Incrementable();     sf.increment();     System.out.println("After sf.increment() called: ");     System.out.println("st1.i = " + st1.i);     System.out.println("st2.i = " + st2.i);     Incrementable.increment();     System.out.println("After Incrementable.increment called: ");     System.out.println("st1.i = " + st1.i);     System.out.println("st2.i = " + st2.i);     } }

练习8：编写一个程序，展示无论你创建了某个特定类的多少个对象，这个类中的某个特定的static域只有一个实例。

// object/OneStaticTest.java // TIJ4 Chapter Object, Exercise 8, page 90 /* Write a program that demonstrates that, no matter how many objects you * create of a particular class, there is only one instance of a particular * static field of that class. */   class StaticTest {     static int i = 47; }   class Incrementable {     static void increment() { StaticTest.i++; } }   public class OneStaticTest {     public static void main(String[] args) {        System.out.println("StaticTest.i= " + StaticTest.i);        StaticTest st1 = new StaticTest();        StaticTest st2 = new StaticTest();        System.out.println("st1.i= " + st1.i);        System.out.println("st2.i= " + st2.i);        Incrementable.increment();        System.out.println("After Incrementable.increment() called: ");        System.out.println("st1.i = " + st1.i);        System.out.println("st2.i = " + st2.i);        Incrementable.increment();        System.out.println("After Incrementable.increment called: ");        System.out.println("st1.i = " + st1.i);        System.out.println("st2.i = " + st2.i);        st1.i = 3;        System.out.println("After st1.i = 3, ");        System.out.println("st1.i = " + st1.i);        System.out.println("st2.i = " + st2.i);        System.out.println("Create another StaticTest, st3.");        StaticTest st3 = new StaticTest();        System.out.println("st3.i = " + st3.i);     } }

练习9：编写一个程序，展示自动包装功能对所有的基本类型和包装器类型都起作用

// TIJ4 Chapter Object, Exercise 9, page 90 // Write a program that demonstrates that autoboxing works for all the primitive // types and their wrappers.   public class AutoboxTest {     public static void main(String[] args) {        boolean b = false;        char c = 'x';        byte t = 8;        short s = 16;        int i = 32;        long l = 64;        float f = 0.32f;        double d = 0.64;        Boolean B = b;        System.out.println("boolean b = " + b);              System.out.println("Boolean B = " + B);        Character C = c;        System.out.println("char c = " + c);        System.out.println("Character C = " + C);        Byte T = t;        System.out.println("byte t = " + t);        System.out.println("Byte T = " + T);        Short S = s;        System.out.println("short s = " + s);        System.out.println("Short S = " + S);        Integer I = i;        System.out.println("int i = " + i);        System.out.println("Integer I = " + I);        Long L = l;        System.out.println("long l = " + l);        System.out.println("Long L = " + L);        Float F = f;        System.out.println("float f = " + f);        System.out.println("Float F = " + F);        Double D = d;        System.out.println("double d = " + d);        System.out.println("Double D = " + D);        } }

练习10：编写一个程序，打印出从命令行获得的三个参数。为此，需要确定命令行数组中String的下标。

// TIJ4 Chapter Object, Exercise 10, page 90 // Write a program that prints three arguments taken from the command line. To do // this you'll need to index into the command-line array of Strings.   public class CommandArgTest_10 {     public static void main(String[] args) {         int[] a = {1, 2, 3};         System.out.println("a[0] = " + a[0]);         System.out.println("a[1] = " + a[1]);         System.out.println("a[2] = " + a[2]);     } }

练习11：将AllTheColorsOfTheRainbow这个示例改写成一个程序，然后编译、运行。

// object/Rainbow.java // TIJ4 Chapter Object, Exercise 11, page 90 // Turn the AllColorsOfTheRainbow into a program that compiles and runs.   public class Rainbow {     public static void main(String[] args) {        AllTheColorsOfTheRainbow atc = new AllTheColorsOfTheRainbow();        System.out.println("atc.anIntegerRepresentingColors = " + atc.anIntegerRepresentingColors);        atc.changeColor(7);        atc.changeTheHueOfTheColor(77);        System.out.println("After color change, atc.anIntegerRepresentingColors = " + atc.anIntegerRepresentingColors);        System.out.println("atc.hue = " + atc.hue);       } }   class AllTheColorsOfTheRainbow {     int anIntegerRepresentingColors = 0;     int hue = 0;     void changeTheHueOfTheColor(int newHue) {        hue = newHue;     }     int changeColor(int newColor) {        return anIntegerRepresentingColors = newColor;           } }

练习12：找出HelloDate.java第二版本，也就是简单注释文档的示例。对该文档执行javadoc，然后通过web浏览器验证所产生的文档。

// object.DocTest.java // TIJ4 Chapter Object, Exercise 12, page 90 /* Find the code for the second version of HelloDate.java, which is the simple * comment documentation example. Execute Javadoc on the file and view the * results with your Web browser. */   import java.util.*;   /** The first Thinking in Java example program. * Displays a string and today's date. * @author Burce Eckel * @author www.MindView.net * @version 4.0 */   public class DocTest {     /** Entry poing to class & application.     * @param args array of string arguments     * @throws exceptions No exceptions thrown     */     public static void main(String[] args) {        System.out.println("Hello, it's: ");        System.out.println(new Date());     } } /* Output: (55% match) */

练习13：通过javadoc运行Documentation1.java、Documentation2.java、Documentation3.java，然后通过web浏览器观看运行结果。

13-1

// object.Documentation1.java // TIJ4 Chapter Object, Exercise 13 - 1 /* Run Documentation1.java, Documentation2.java and Documentation3.java * through Javadoc. Verify the resulting documentation with your Web browser. */   /** A class comment */ public class Documentation1 {     /** A field comment */     public int i;     /** A method comment */     public void f() {} }

13-2

// object.Documentation1.java // TIJ4 Chapter Object, Exercise 13 - 2 /* Run Documentation1.java, Documentation2.java and Documentation3.java * through Javadoc. Verify the resulting documentation with your Web browser. */ import java.util.*;   // object/Documentation2.java /** * * Uses * System.out.println(new Date()); * */   public class Documentation2 {     Date d = new Date();     void showDate() {      System.out.println("Date = " + d);     } }

13-3

// object.Documentation1.java // TIJ4 Chapter Object, Exercise 13 - 3 /* Run Documentation1.java, Documentation2.java and Documentation3.java * through Javadoc. Verify the resulting documentation with your Web browser. */ import java.util.*;   // object/Documentation3.java /** * You can even insert a list: * * Item one * Item two * Item three * */   public class Documentation3 {     public static void main(String[] args) {        Date d = new Date();        System.out.println("d = " + d);     } }

练习14：在前一个练习的文档中加入各项的HTML列表

// object/Documentation4.java // TIJ4 Chapter Object, Exercise 14, page 90 // Add an HTML list of items to the documentation in the previous exercise. import java.util.*;   // object/Documentation4.java /** * You can even insert a list: * * Item one * Item two * Item three *                   * Another test list        *        * One        * Two        * Three        *        */    public class Documentation4 {          /** Let's try a public field list        *        * One        * Two        * Three        *        */                public int i = 2;          /**        * A private field list (-private to see)        *        * One        * Two        * Three        *        */           private int j = 3;          /**        * Another list can be inserted here to help explain the        * following method call        *        * One        * Two        * Three        *        * but may be formatted differently in Method Summary        */        public static void main(String[] args) {          /**        * Let's try another test list here        *        * One        * Two        * Three        *        */           Date d = new Date();        System.out.println("d = " + d);     } }

练习15：使用练习2的程序，加入注释文档，用javadoc提取此注释文档，并产生一个HTML文件，然后通过web浏览器查看结果。

// object/HelloDocTest.java // TIJ4 Chapter Object, Exercies 15, page 91 /* Take the program in Exercise 2 and add comment documentation to it. Extract * this comment documentation into an HTML file using Javadoc and view it with * your Web browser. */     /** * Public class contained in file of the same name that includes main() */   public class HelloDocTest {       /** main method executed by java     */        public static void main(String[] args) {     System.out.println("Hello World!");     } }

练习16：找到第5章中的Overloading.java示例，并为它加入javadoc文档，然后用javadoc提取此注释文档，并产生一个HTML文件，最后，通过web浏览器查看结果。

// object/Overloading.java // TIJ4 Chapter Object, Exercise 16, page 91 /* In the Initialization and Cleanup chapter, locate the Overloading.java * example and add Javadoc documentation. Extract this comment documentation * into and HTML file using Javadoc and view it with your Web browser. */   // initialization/Overloading.java // Demonstration of both constructor // and ordinary method overloading.   /** creates type Tree wth two constructors and one info method */   class Tree {     int height;         /** no-argument constructor     * assigns height = 0     */       Tree() {        System.out.println("Planting a seedling");        height = 0;     }       /** constructor taking an int argument,     * assigns height that int argument     */       Tree(int initialHeight) {        height = initialHeight;        System.out.println("Creating new tree that is " + height + " feet tall");     }       /** method to print height of tree object     */         void info() {        System.out.println("Tree is " + height + " feet tall");     }       /** overloaded method to print string argument     * and height of a tree object     */       void info(String s) {        System.out.println(s + ": Tree is " + height + " feet tall");     } }   /** class to test construction of tree objects */   public class Overloading {     public static void main(String[] args) {        for(int i = 0; i < 5; i++) {            Tree t = new Tree(i);            t.info();            t.info("overloading method");        }        // Overloaded constructor:        new Tree();     } }