Java程序设计基础——课本例题

第三章

1.数据类型的自动转换App3_1

源代码：

//filename:App3_1.java
public class App3_1
{
   
    public static void main (String[] args)
    {
   
        int a = 155;
        float b = 21.0f;
        System.out.println("a = " + a + ",b = "+ b);
        System.out.println("a/b = " + (a/b));
    }
}

编译运行：

2.整型与浮点数据类型的转换App3_2

源代码：

//filename:App3_2.java  整数与浮点数的类型转换
public class App3_2
{
   
    public static void main(String[] args)
    {
   
        int a = 155;
        int b = 9;
        float g,h;
        System.out.println("a = " + a + ",b = " + b);  // 输出a，b的值
        g = a/b;  //将a除以b的结果放在g中
        System.out.println("a/b = " + g + "\n");  //输出g的值
        System.out.println("a = " + a + ",b = " + b);  // 输出a，b的值
        h = (float)a/b;  //先将a强制转换成float类型后再参加运算
        System.out.println("a/b = " + h);  //输出h的值
        System.out.println("(int)h = " + (int)h);  //将变量h强制转换成int型

    }    
}

编译运行：

3.从键盘输入数据App3_3和App3_3_1

App3_3源代码：

//filename:App3_3.java  由键盘输入字符串
import java.io.*;  //加载java.io类库里的所有类
public class App3_3
{
   
    public static void main(String[] args) throws IOException
    {
   
        BufferedReader buf;
        String str;
        buf = new BufferedReader(new InputStreamReader(System.in));
        System.out.print("请输入字符串：");  //输出字符串
        str = buf.readLine();  //将输入的文字指定给字符串变量str存放
        System.out.println("您输入的字符串是：" + str);  //输出字符串
    }
}

App3_3编译运行：

App3_3_1源代码：

//filename:App3_3_1.java  由键盘输入字符串
import java.io.*;  //加载java.io类库里的所有类
public class App3_3_1
{
   
    public static void main(String[] args) throws IOException
    {
   
        BufferedReader buf;
        char str;
        buf = new BufferedReader(new InputStreamReader(System.in));
        System.out.print("请输入字符串：");  //输出字符串
        str = (char)buf.read();  //将输入的文字指定给字符串变量str存放
        System.out.println("您输入的字符串是：" + str);  //输出字符串
    }
}

App3_3_1编译运行：

4.从键盘输入数字，然后将其转换成数值型数据App3_4

源代码：

//filename:App3_4.java  //由键盘输入整数
import java.io.*;
public class App3_4
{
   
    public static void main(String[] args) throws IOException
    {
   
        float num;
        String str;
        BufferedReader buf;
        buf = new BufferedReader(new InputStreamReader(System.in));
        System.out.print("请输入一个实数：");
        str = buf.readLine();  //将输入的文字指定给字符串变量str存放
        num = Float.parseFloat(str);  //将str转换成float类型后赋给num
        System.out.println("您输入的数为：" + num);
    }
}

编译运行：

5.从键盘输入多个数据App3_5

源程序：

//filename:App3_5.java  由键盘输入多个数据
import java.io.*;
public class App3_5
{
   
    public static void main(String[] args) throws IOException
    {
   
        int num1,num2;
        String str1,str2;
        InputStreamReader in;
        in = new InputStreamReader(System.in);
        BufferedReader buf;
        buf = new BufferedReader(in);
        System.out.print("请输入一个数：");
        str1 = buf.readLine();  //将输入的内容赋值给字符串变量str1
        num1 = Integer.parseInt(str1);  //将str1转成int类型后赋给num1
        System.out.