Thinking in Java - Fourth Edition 章节练习个人解答——第5章

 注：本练习题答案系个人阅读后所作解答，非原书所配答案。（由于水平有限，文中出现错误还望谅解与指正）

 

文中所有源代码皆在Eclipse-jee-indigo-3.7，Java SE 6平台下测试运行。

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练习1：

package lib.fifth;public class Exercise_1 {String s;Exercise_1() {}public static void main(String[] args) {Exercise_1 e = new Exercise_1();System.out.print(e.s);}} /* Output:null*///:~

练习2：

package lib.fifth;public class Exercise_2 {String s = "abc";Exercise_2() {System.out.println(s + " (No-arguments)");}Exercise_2(String s) {System.out.println(this.s + " (Arguments)");this.s = s;}public static void main(String[] args) {Exercise_2 e1 = new Exercise_2();Exercise_2 e2 = new Exercise_2("bcd");System.out.println(e1.s + " (No-arg created)");System.out.println(e2.s + " (Arguments created)");}} /* Output:abc (No-arguments)abc (Arguments)abc (No-arg created)bcd (Arguments created)*///:~

练习3：

package lib.fifth;public class Exercise_3 {Exercise_3() {System.out.print("Hello!");}public static void main(String[] args) {new Exercise_3();}} /* Output:Hello!*///:~

练习4：

package lib.fifth;public class Exercise_4 {Exercise_4() {System.out.print("Hello!");}Exercise_4(String s) {System.out.print("Hello! " + s);}public static void main(String[] args) {new Exercise_4("Overloaded constructor");}} /* Output:Hello! Overloaded constructor*///:~

练习5：

package lib.fifth;public class Dog {void bark(int i) {System.out.println("barking!");}void bark(float f) {System.out.println("howling!");}public static void main(String[] args) {Dog dog = new Dog();dog.bark(1);dog.bark(1f);}} /* Output:barking!howling!*///:~

练习6：

package lib.fifth;public class Dog2 {void bark(int i) {System.out.println("barking!");}void bark(float f) {System.out.println("howling!");}public static void main(String[] args) {Dog2 dog = new Dog2();dog.bark(1f);dog.bark(1);}} /* Output:howling!barking!*///:~

练习7：

package lib.fifth;public class Exercise_7 {int a;public static void main(String[] args) {Exercise_7 e = new Exercise_7();System.out.print(e.a);}} /* Output:0*///:~

练习8：

package lib.fifth;public class Exercise_8 {void pick() {pit();this.pit();}void pit() {System.out.println("Hello!");}public static void main(String[] args) {Exercise_8 e = new Exercise_8();e.pick();}} /* Output:Hello!Hello!*///:~

练习9：

package lib.fifth;public class Exercise_9 {Exercise_9() {System.out.print("abc");}Exercise_9(String s) {this();}public static void main(String[] args) {new Exercise_9("");}} /* Output:abc*///:~

练习10：

package lib.fifth;public class Exercise_10 {protected void finalize(){System.out.print("Look out!");}public static void main(String[] args) {new Exercise_10();}} /* (Execute to see output) *///:~

 

练习11：

package lib.fifth;public class Exercise_11 {protected void finalize(){System.out.print("Look out!");}public static void main(String[] args) {new Exercise_10();System.gc();}} /* Output:Look out!*///:~

练习12：

package lib.fifth;import java.util.Random;public class Tank {int status;Tank() {}Tank(int status) {this.status = status;}protected void finalize() {System.out.print(status + " ");System.out.println(status == 0);}public static void main(String[] args) {for(int i = 0; i < 100;) {Random rand = new Random();int j = rand.nextInt(2);if(j == 0)i++;new Tank(j);}System.gc();}} /* (Execute to see output) *///:~

练习13：

package lib.fifth;import static net.util.Print.print;class Cup {Cup(int marker) {print("Cup(" + marker + ")");}void f(int marker) {print("f(" + marker + ")");}}class Cups {static Cup cup1;static Cup cup2;static {cup1 = new Cup(1);cup2 = new Cup(2);}Cups() {print("Cups()");}}public class Exercise_13 {public static void main(String[] args) {print("Inside main()");// Cup.cup1.f(99);  // (1)}static Cups cup1 = new Cups();  // (2)static Cups cup2 = new Cups();  // (2)} /* Output:Cup(1)Cup(2)Cups()Cups()Inside main()*///:~

练习14：

package lib.fifth;public class Exercise_14 {static String s1 = "abc";static String s2;static {s2 = "xyz";}static void print() {System.out.println(s1);System.out.println(s2);}public static void main(String[] args) {print();}} /* Output:abcxyz*///:~

练习15：

package lib.fifth;public class Exercise_15 {String s;{s = "abc";}public static void main(String[] args) {Exercise_15 e = new Exercise_15();System.out.print(e.s);}} /* Output:abc*///:~

练习16：

package lib.fifth;public class Exercise_16 {public static void main(String[] args) {String[] s = new String[]{"fiddle", "de", "dum" };for(String str : s)System.out.print(str + " ");}} /* Output:fiddle de dum *///:~

练习17：

package lib.fifth;public class Exercise_17 {Exercise_17(String s) {System.out.print(s);}public static void main(String[] args) {Exercise_17[] e;}} ///:~

练习18：

package lib.fifth;public class Exercise_18 {Exercise_18(String s) {System.out.println(s);}public static void main(String[] args) {Exercise_18[] e = new Exercise_18[]{new Exercise_18("fiddle"),new Exercise_18("de"),new Exercise_18("dum"),};}} /* Output:fiddlededum*///:~

练习19：

package lib.fifth;import java.util.Arrays;public class Exercise_19 {static void f(String...s) {System.out.println(Arrays.toString(s));}public static void main(String[] args) {f("fiddle", "de", "dum");f(new String[]{"fiddle", "de", "dum"});}} /* Output:[fiddle, de, dum][fiddle, de, dum]*///:~

练习20：

package lib.fifth;import java.util.Arrays;public class Exercise_20 {public static void main(String...args) {System.out.print(Arrays.toString(args));}} /* Input:fiddle de dumOutput:[fiddle, de, dum]*///:~

练习21：

package lib.fifth;public enum Value {$1, $2, $5, $10, $20, $50} ///:~

package lib.fifth;public class Exercise_21 {public static void main(String[] args) {for(Value v : Value.values())System.out.println(v + ", ordinal " + v.ordinal());}} /* Output:$1, ordinal 0$2, ordinal 1$5, ordinal 2$10, ordinal 3$20, ordinal 4$50, ordinal 5*///:~

练习22：

package lib.fifth;public class Exercise_22 {Value v;Exercise_22(Value v) {this.v = v;}String describe() {switch(v) {case $1: return "$1: Front: the 1th US President, George Washington.";case $2: return "$2: Front: the 3th US President, Thomas Jefferson.";case $5: return "$5: Front: the 16th US President, Abraham Lincoln.";case $10: return "$10: Front: the 1th US Treasury Secretary, Alexander Hamilton.";case $20: return "$20: Front: the 7th US president, Andrew Jackson.";case $50: return "$50: Front: the 18th US president, Ulysses Simpson Grant.";default: return null;}}public static void main(String[] args) {System.out.println(new Exercise_22(Value.$1).describe());System.out.print(new Exercise_22(Value.$5).describe());}} /* Output:$1: Front: the 1th US President, George Washington.$5: Front: the 16th US President, Abraham Lincoln.*///:~

 

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