Thinking in Java
Here is some answers of Thinking in Java, during the time i am studying Java, I find lots of differences and improvements between C++. I try my best to finish all questions behind every chapters, because I think the best way to study a programming language is to code as much as can. And here they are, these questions can be good practices for me to train my coding ability. last update: 19_06_10
Chapter 3
Test 2 & 3
创新一个包含一个float的类，并用这个类来展现别名机制。
public class Main {
public static void main(String[] args) {
Test test1 = new Test();
Test test2 = new Test();
System.out.println("Init data:");
System.out.println("test1.i = " + test1.i);
System.out.println("test2.i = " + test2.i);
System.out.println("use class.value = class.value:");
test1.i = test2.i = 100;
System.out.println("test1.i = " + test1.i);
System.out.println("test2.i = " + test2.i);
System.out.println("use class = class:");
test1 = test2;
test1.i = 45;
System.out.println("test1.i = " + test1.i);
System.out.println("test2.i = " + test2.i);
}
}
class Test {
float i = 12.0f;
}
Test 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 Main {
public static void main(String[] args) {
double Speed = 12.1;
double time = 60;
System.out.println(Speed * time);
}
}
Test 5
创建一个名为Dog的类，它包含两个String域，name和says。 在main()方法种，创建两个Dog对象，一个名为Spot（它的叫声为“Ruff！”）另一个名为scruffy（它的叫声为“Wurf！”）然后显示它们的名字和叫声。
public class Main {
public static void main(String[] args) {
Dog spot = new Dog("spot", "Ruff!");
Dog scuffy = new Dog("scuffy","Wurf!");
System.out.println("Name is " + spot.name + ", says: " + spot.says);
System.out.println("Name is " + scuffy.name + ", says: " + scuffy.says);
}
}
class Dog {
public
String name;
public
String says;
Dog(String name, String says)
{
this.name = name;
this.says = says;
}
}
Test 6
创建一个新的Dog的索引，并对其赋值为spot对象，测试用==和equals（）来比较所有引用的效果
public class Main {
public static void main(String[] args) {
Dog spot = new Dog("spot", "Ruff!");
Dog spot1 = new Dog();
spot1.says = spot.says;
spot1.name = spot.name;
System.out.println("use == : ");
System.out.println(spot == spot1);
System.out.println("use equal");
System.out.println(spot.equals(spot1));
}
}
Test 7
编写一个程序模拟扔硬币的结果
import java.util.*;
public class Main {
public static void main(String[] args) {
Random rand = new Random();
int i;
int index = 0;
while (index != 10) {
i = rand.nextInt(2);
switch (i) {
case 1:
System.out.println("head");
break;
case 0:
System.out.println("tail");
break;
default:
System.out.println("wrong random");
break;
}
index++;
}
}
}
Test 8
使用 十六进制和八进制来操作long值。
public class Main {
public static void main(String[] args) {
long l = 0xFFFFF;
long l1 = 011111;
System.out.println(Long.toBinaryString(l) + " " + l);
System.out.println(Long.toBinaryString(l1) + " " + l1);
}
}
Test 9
分别显示float和double使用指数计数法表示的最大值和最小值
public class Main {
public static void main(String[] args) {
System.out.println("Max value of float :" + Float.MAX_VALUE);
System.out.println("Min value of float :" + Float.MIN_VALUE);
System.out.println("Max value of double :" + Double.MAX_VALUE);
System.out.println("Min value of double :" + Double.MIN_VALUE);
}
}
Test 10
一个具有交替的1和0，最低有效位为0，另一个最低有效位为1，使用位操作的所有方式结合他们
public class Main {
public static void main(String[] args) {
String s = "10101010101010";
String s1 = "101010101010101";
int i = Integer.parseInt(s, 2);
int i1 = Integer.parseInt(s1, 2);
System.out.println("^ : " + (i ^ i1) + " " + Integer.toBinaryString((i ^ i1)));
System.out.println("| : " + (i | i1) + " " + Integer.toBinaryString((i | i1)));
System.out.println("& : " + (i & i1) + " " + Integer.toBinaryString((i & i1)));
System.out.println("~ : " + (~i1) + " " + Integer.toBinaryString(~i1));
System.out.println("~ : " + (~i) + " " + Integer.toBinaryString(~i));
}
}
Test 11
最高位有效数字为1的数字开始，向右移位，知道所有二进制位都被移出为止
public class Main {
public static void main(String[] args) {
String s = "111110111";
int i = Integer.parseInt(s, 2);
while(i != 0)
{
i >>= 1;
System.out.println(i + " - " + Integer.toBinaryString(i));
}
}
}
Test 12
所有位为1的数开始，先左移，然后右移，直到所有都被移出为止
public class Main {
public static void main(String[] args) {
String s = "111111111";
int i = Integer.parseInt(s, 2);
i <<= 3;
System.out.println(i + " - " + Integer.toBinaryString(i));
while(i != 0)
{
i >>= 1;
System.out.println(i + " - " + Integer.toBinaryString(i));
}
}
}
Test 13
以二进制形式显示char类型的值
public class Main {
public static void main(String[] args) {
char a[] = {'a', 'b', 'c', 'd'};
for (int i : a) {
System.out.println((char)i + " - " + i + " - " + Integer.toBinaryString(i));
}
}
}
Chapter 4
Test 1
打印1到100的值
public class Main {
public static void main(String[] args) {
for(int i = 1; i <= 100; i++)
{
System.out.print(i + " ");
if((i % 10) == 0)
{
System.out.println();
}
}
}
}
Test 2 & 3
生成25个随机数，判断与下一个数的关系（大于，小于，等于）
This question should be worth to think about it. Java do not let you use some code like this below
int r;
for(...)
print(r);
That will cause an error, r might not be initialized. if you are familiar with C or C++, you maybe thought this code should be ok, but java does not allow it. Java ask you to initialize and define any value before you use it.
import java.util.Random;
public class Main {
public static void main(String[] args) {
Random rand = new Random();
int r, temp = 0;
r = rand.nextInt(100);
System.out.println("The begin number is " + r);
temp = r;
for (int i = 0; i < 25; i++) {
if (i == 0) {
;
} else {
r = rand.nextInt(100);
if (r > temp)
System.out.println("No." + i + ", this time number is " + temp +
", and next time the number is " + r +
", and the status is Smaller");
else if (r == temp)
System.out.println("No." + i + ", this time number is " + temp +
", and next time the number is " + r +
", and the status is equal");
else
System.out.println("No." + i + ", this time number is " + temp +
", and next time the number is " + r +
", and the status is larger");
temp = r;
}
}
System.out.println("No.25, the final number is " + r);
}
}
Test 4
只用2层for和%找出素数
import java.util.Random;
public class Main {
public static void main(String[] args) {
Chapter4 c = new Chapter4();
c.CheckPrimeNumber0ToInput(0);
}
}
class Chapter4 {
//you should type a number which is larger than 0
void CheckPrimeNumber0ToInput(int num) {
int isPrimeNumber = 0;
for (int j = 0; j <= num; j++) {
if (j == 1 || j == 0)
isPrimeNumber = 1;
else {
for (int i = 2; i < j; i++)
if ((j % i) == 0)
isPrimeNumber++;
}
if (isPrimeNumber == 0)
System.out.println(j + " is Prime Number");
else
System.out.println(j + " is not Prime Number");
isPrimeNumber = 0;
}
}
}
Test 5
略
Test 6
增加两个参数，判断输入是否是在他们之间
public class Main {
static int test(int testval, int target, int begin, int end)
{
int returnValue = 0;
if(testval > target)
returnValue = 1;
else if (testval < target)
returnValue = -1;
else
returnValue = 0;
if(testval <= end && testval >= begin)
System.out.println("test value is within the range");
else
System.out.println("test value is not within the range");
return returnValue;
}
public static void main(String[] args) {
System.out.println(test(5,10,2,8));
System.out.println(test(5,0,1,3));
}
}
Test 7
使用break 和return 打到99
// break
public class Main {
static void test() {
for (int i = 1; i <= 100; i++) {
System.out.print(i + " ");
if ((i % 10) == 0) {
System.out.println();
}
if (i == 99)
break;
}
}
public static void main(String[] args) {
test();
}
}
// return
public class Main {
static void test() {
for (int i = 1; i <= 100; i++) {
System.out.print(i + " ");
if ((i % 10) == 0) {
System.out.println();
}
if (i == 99)
return;
}
}
public static void main(String[] args) {
test();
}
}
Test 8
写一个switch 开关，放入for中测试每次的情况，测试有break和没有break的区别
// with break
public class Main {
public static void main(String[] args) {
for (int i = 0; i != 3; i++) {
switch (i) {
case 0:
System.out.println("First");
break;
case 1:
System.out.println("Second");
break;
case 2:
System.out.println("Third");
break;
}
}
}
}
public class Main {
public static void main(String[] args) {
for (int i = 0; i != 3; i++) {
switch (i) {
case 0:
System.out.println("First");
case 1:
System.out.println("Second");
case 2:
System.out.println("Third");
}
}
}
}
Test 9
输出斐波那契数列
public class Main {
public static void main(String[] args) {
Fibonacci f = new Fibonacci(5);
}
}
class Fibonacci {
Fibonacci(int index) {
for (int i = 1; i <= index; i++) {
System.out.println(fibonacci(i));
}
}
int fibonacci(int i) {
if (i == 1 || i == 2)
return 1;
else
return fibonacci((i - 1)) + fibonacci((i - 2));
}
}
Test 10
输出4位数的吸血鬼数
In this question, I made a big mistake, I should use method to replace the codes, because they are nearly same. (method in some way can help you type less code and make it readable).
for example:
((ones * 10 + tens) * (hundreds * 10 + thousands) == i)
I should add the new methods:
static int multiply(int i, int j)
{
return i * 10 + j;
}
static boolean check(int number, int i, int j)
{
return number == (i * j);
}
static void print(int ones, int tens, int hundreds, int thousands)
{
System.out.println("The Vampire number is " + i +
" --" + ones + tens + " * " + hundreds + thousands);
}
and replace my code like this:
// ....
// In this way, you can make your code look well and readable.
if(check(i, multiply(ones, tens), multiply(hundreds, thousands)))
print(ones, tens, hundreds, thousands);
// ....
and here is my old answer. pretty messy.
public class Main {
public static void main(String[] args) {
VampireNumber v = new VampireNumber();
v.vampireNumber();
}
}
class VampireNumber {
void vampireNumber() {
int ones, tens, hundreds, thousands;
for (int i = 1000; i < 10000; i++) {
ones = i % 10;
tens = i / 10 % 10;
hundreds = i / 100 % 10;
thousands = i / 1000;
if(ones == 0 && tens == 0)
continue;
// 1
if ((ones * 10 + tens) * (hundreds * 10 + thousands) == i)
{
System.out.println("The Vampire number is " + i +
" --" + ones + tens + " * " + hundreds + thousands);
}
// 2
else if ((ones * 10 + tens) * (thousands * 10 + hundreds) == i)
{
System.out.println("The Vampire number is " + i +
" --" + ones + tens + " * " + thousands + hundreds);
}
// 3
else if ((ones * 10 + hundreds) * (tens * 10 + thousands) == i)
{
System.out.println("The Vampire number is " + i +
" --" + ones + hundreds + " * " + tens + thousands);
}
// 4
else if ((ones * 10 + hundreds) * (thousands * 10 + tens) == i)
{
System.out.println("The Vampire number is " + i +
" --" + ones + hundreds + " * " + thousands + tens);
}
// 5
else if ((ones * 10 + thousands) * (tens * 10 + hundreds) == i)
{
System.out.println("The Vampire number is " + i +
" --" + ones + thousands + " * " + tens + hundreds);
}
// 6
else if ((ones * 10 + thousands) * (hundreds * 10 + tens) == i)
{
System.out.println("The Vampire number is " + i +
" --" + ones + thousands + " * " + hundreds + tens );
}
// 21 34
else if ((tens * 10 + ones) * (hundreds * 10 + thousands) == i)
{
System.out.println("The Vampire number is " + i +
" --" + tens + ones + " * " + hundreds + thousands);
}
// 23 41
else if ((tens * 10 + hundreds) * (thousands * 10 + ones) == i)
{
System.out.println("The Vampire number is " + i +
" --" + tens + hundreds + " * " + thousands + ones);
}
// 24 31
else if ((tens * 10 + thousands) * (hundreds * 10 + ones) == i)
{
System.out.println("The Vampire number is " + i +
" --" + tens + thousands + " * " + hundreds + ones);
}
// 31 42
else if ((hundreds * 10 + ones) * (thousands * 10 + tens) == i)
{
System.out.println("The Vampire number is " + i +
" --" + hundreds + ones + " * " + thousands + tens);
}
// 32 41
else if ((hundreds * 10 + tens) * (thousands * 10 + ones) == i )
{
System.out.println("The Vampire number is " + i +
" --" + hundreds + tens + " * " + thousands + ones);
}
}
}
}
Chapter 5
Test 1
创建类，包含一个string，验证被初始化为了null
public class Main {
public static void main(String[] args) {
Test t = new Test();
if(t.str == null)
System.out.println("It's null");
else
System.out.println("It isn't null");
}
}
class Test {
String str;
}
Test 2
创建类，判断差异，一个string在定义时被初始化，一个通过构造器初始化
public class Main {
public static void main(String[] args) {
Test t = new Test("a value");
System.out.println("t.str " + t.str);
System.out.println("t.testStr " + t.testStr);
Test t1 = new Test();
System.out.println("t1.str " + t1.str);
System.out.println("t1.testStr " + t1.testStr);
t1.str = "131";
t1.testStr = "13123";
System.out.println("t1.str " + t1.str);
System.out.println("t1.testStr " + t1.testStr);
}
}
class Test {
String str = "get";
String testStr;
Test(String testStr)
{
this.testStr = testStr;
}
Test()
{
}
}
Test 3
创建一个默认构造器，打印一行话
public class Main {
public static void main(String[] args) {
Test t = new Test();
}
}
class Test {
Test() {
System.out.println("This is a sentence");
}
}
Test 4
为上一个问题添加一个重载的构造器，接受一个字符串参数，把自己的话和新增的话打印出来
public class Main {
public static void main(String[] args) {
Test t = new Test();
Test t1 = new Test("again??");
}
}
class Test {
Test() {
System.out.println("This is a sentence");
}
Test(String str)
{
System.out.println("This is a sentence. " + str);
}
}
Test 5
创建一个Dog类，有一个重载的bark()方法，打印不同类型的狗吠barking，咆哮 howling
public class Main {
public static void main(String[] args) {
Dog myDog = new Dog(1);
Dog yourDog = new Dog("1");
}
}
class Dog {
Dog(int i) {
System.out.println("Barking");
}
Dog(String str) {
System.out.println("Howling");
}
}
Test 6
设置2个参数来实现重载，但是顺序不同，判断是否工作
Because java does not Implicit convert data type, so these codes will all be fine to Java. But if you were writing C++ code, you should pay much attention on these.
public class Main {
public static void main(String[] args) {
Dog dog1 = new Dog(1,1);
Dog dog2 = new Dog(1,1.0);
Dog dog3 = new Dog(1.0,1.0);
Dog dog4 = new Dog(1.0f,1.0);
Dog dog5 = new Dog(1.0,1.0f);
Dog dog6 = new Dog(1,1.0f);
Dog dog7 = new Dog(1.0f,1);
Dog dog8 = new Dog(1.0,1);
Dog dog9 = new Dog(1,1l);
Dog dog10 = new Dog(1l,1);
}
}
class Dog {
Dog(int i,float j) {
System.out.println("int float");
}
Dog(double i, double j) {
System.out.println("double double");
}
Dog(int i, int j) {
System.out.println("int int");
}
Dog(int i, double j) {
System.out.println("int double");
}
Dog(float i, int j) {
System.out.println("float int");
}
Dog(double i, int j) {
System.out.println("double int");
}
Dog(int i, long j) {
System.out.println("int long");
}
Dog(long i, int j) {
System.out.println("long int");
}
Dog(float i, double j) {
System.out.println("float double");
}
Dog(double i, float j) {
System.out.println("double float");
}
}
Test 7
创建一个没有构造器的类，在main中创建对象，验证是否有自动加入了默认构造器
public class Main {
public static void main(String[] args) {
Dog dog = new Dog();
System.out.println("Work well");
}
}
class Dog {
}
Test 8
写一个有2个方法的类，调用方法2次，一次单纯调用，一次使用this
public class Main {
public static void main(String[] args) {
Dog dog = new Dog();
dog.g();
}
}
class Dog {
void f()
{
System.out.println("It's a test");
}
void g()
{
f();
this.f();
}
}
Test 9
编写2个重载构造器，一个调用另外的一个
public class Main {
public static void main(String[] args) {
Dog dog = new Dog();
Dog dog1 = new Dog("Java");
}
}
class Dog {
Dog() {
this("C++");
System.out.println("Good baby\n");
}
Dog(String str) {
System.out.println("I like " + str.replace("Java", "C++"));
}
}
Test 10 - 12
略
Test 13
验证段落中的语句
class Cup {
Cup(int marker) {
System.out.println("Cup(" + marker + ")");
}
void f(int marker) {
System.out.println("f(" + marker + ")");
}
}
class Cups {
static Cup cup1;
static Cup cup2;
static {
cup1 = new Cup(1);
cup2 = new Cup(2);
}
Cups() {
System.out.println("Cups()");
}
}
public class Main {
public static void main(String[] args) {
System.out.println("Inside main()");
Cups.cup1.f(99);
}
static Cups cups1 = new Cups();
//static Cups cups2 = new Cups();
}
Test 14
编写一个类，拥有2个字符串域，一个在定义的时候初始化，一个在静态块中初始化，加入一个静态方法，打印他们的值，证明，他们会在使用之前完成初始化的动作
class Test14 {
static String s = "s";
static String s1;
static {
s1 = "s1";
System.out.println("s1 is initialized");
}
static void f() {
System.out.println(s + " and " + s1);
}
}
public class Main {
public static void main(String[] args) {
System.out.println("Inside main()");
Test14.f();
}
}