Java程式設計思想第五章習題
阿新 • • 發佈：2018-12-22
練習一：驗證未被初始化的引用被初始化成了null
package thinking.java.chapter05;
public class Demo01 {
public static void main(String[] args) {
class Person{
String a;
Person(){
System.out.println(a);
}
}// TODO Auto-generated method stub
new Person();
}
}
練習二：
package thinking.java.chapter05; public class Demo02 { public static void main(String[] args) { // TODO Auto-generated method stub class Student{ String stu1; Student(){ String stu2 = null; System.out.println(stu1); System.out.println(stu2); } } new Student(); } }
練習三：
package thinking.java.chapter05;
public class Demo03 {
public static void main(String[] args) {
class A{
A(){
System.out.println("呼叫無參構造器");
}
}
A a = new A();
}
}
練習4：
package thinking.java.chapter05; public class Demo03 { public static void main(String[] args) { class A{ A(){ System.out.println("呼叫無參構造器"); } A(String a){ System.out.println("呼叫有參構造器"+a); } } A a = new A(); A aa = new A("TIFFANY"); } }
練習5：
package thinking.java.chapter05; public class Demo05 { public static void main(String[] args) { class Dog{ public void bark(int a){ System.out.println("barking"); } public void bark(String b) { System.out.println("howling"); } } Dog d = new Dog(); d.bark(1); d.bark("a"); } }
練習6：
package thinking.java.chapter05;
public class Demo05 {
public static void main(String[] args) {
class Dog{
public void bark(int a,String b){
System.out.println("barking");
}
public void bark(String b,int a) {
System.out.println("howling");
}
}
Dog d = new Dog();
d.bark(1,"a");
d.bark("a",1);
}
}
練習8：
package thinking.java.chapter05;
public class Demo6 {
public static void main(String[] args) {
class Person{
int i = 0;
public int p1(Person per){
per.p2(p2(this));
return i;
}
public Person p2(Person per) {
i++;
return per;
}
}
Person per = new Person();
System.out.println(per.p1(per));
}
}
練習9：
package thinking.java.chapter05;
public class Demo09 {
public static void main(String[] args) {
class Flower{
int count = 0;
String aa = "rose";//不能在非靜態的類中宣告靜態變數
Flower(String aa){
count++;
System.out.println(count+" "+aa);
}
public Flower(String aa,int count) {
this(aa);
}
}
Flower flower = new Flower("lily",2);
}
}
練習16：
package thinking.java.chapter05;
public class Demo16 {
public static void main(String[] args) {
String[] s = new String[] {
new String("tiffany"),
new String("jeff"),
new String("sarah"),
};
for(String a:s) {
System.out.println(a);
}
}
}
練習17：
package thinking.java.chapter05;
class Persan{
Persan(String name){
System.out.println("姓名是："+name);
}
}
public class Demo17 {
public static void main(String[] args) {
Persan[] p = new Persan[] {};
// 並不會列印初始化的訊息，因為壓根沒有建立物件，不會呼叫構造器
}
}
練習18：
package thinking.java.chapter05;
class Persan{
Persan(String name){
// String name = "tiffany";
System.out.println("姓名是："+name);
}
}
public class Demo17 {
public static void main(String[] args) {
Persan[] p = new Persan[] {new Persan("tiffany")};//通過建立一個Persan物件來呼叫構造器
// 並不會列印初始化的訊息，因為壓根沒有建立物件，不會呼叫構造器
}
}
練習21：
package thinking.java.chapter05;
//可以將enum理解成一個類，因為它由自己的方法，所以在外部不能宣告為public
enum Money{
ONE,TWO,FIVE,TEN,FIVTY,HUNDRED,
}
public class Demo21 {
public static void main(String[] args) {
for(Money m:Money.values())
System.out.println(m+" ordinal "+m.ordinal());
}
}
練習22：
package thinking.java.chapter05;
//可以將enum理解成一個類，因為它由自己的方法，所以在外部不能宣告為public
enum Money{
ONE,TWO,FIVE,TEN,FIVTY,HUNDRED,
}
public class Demo21 {
Money money;
public Demo21(Money money) {
this.money = money;
}
public void describe() {
System.out.println("the num is:");
switch(money) {
case ONE:
System.out.println("one yuan");
break;
case TWO:
System.out.println("two yuan");
break;
case FIVE:
System.out.println("five yuan");
break;
case TEN:
System.out.println("ten yuan");
break;
case FIVTY:
System.out.println("fivty yuan");
break;
case HUNDRED:
System.out.println("one hundred yuan");
break;
default:
System.out.println("not found");
}
}
public static void main(String[] args) {
// for(Money m:Money.values())
// System.out.println(m+" ordinal "+m.ordinal());
Demo21
one = new Demo21(Money.ONE);
one.describe();
}
}