java.io包提供了各种类来读取来自各种源和目标的写入数据。
您可以使用各种类（例如Scanner，BufferedReader，InputStreamReader，Console等）从用户（键盘）读取数据。
从Java 1.5开始引入Scanner类。此类接受File，InputStream，Path和String对象，使用正则表达式逐个令牌读取所有原始数据类型和String（从给定的源）令牌。默认情况下，空格被视为定界符（将数据分成令牌）。
要从键盘读取数据，您需要使用标准输入作为源(System.in)。对于每个数据类型的nextXXX()被设置，即，nextInt()，nextShort()，nextFloat()，nextLong()，nextBigDecimal()，nextBigInteger()，nextLong()，nextShort()，nextDouble()，nextByte()，nextFloat()，next()。
以下Java程序使用Scanner类从用户读取数据。
import java.util.Scanner;
class Student{
String name;
int age;
float percent;
boolean isLocal;
char grade;
Student(String name, int age, float percent, boolean isLocal, char grade){
this.name = name;
this.age = age;
this.percent = percent;
this.isLocal = isLocal;
this.grade = grade;
}
public void displayDetails(){
System.out.println("Details..............");
System.out.println("Name: "+this.name);
System.out.println("Age: "+this.age);
System.out.println("Percent: "+this.percent);
if(this.isLocal) {
System.out.println("Nationality: Indian");
}else {
System.out.println("Nationality: Foreigner");
}
System.out.println("Grade: "+this.grade);
}
}
public class ReadData {
public static void main(String args[]) {
Scanner sc =new Scanner(System.in);
System.out.println("Enter your name: ");
String name = sc.next();
System.out.println("Enter your age: ");
int age = sc.nextInt();
System.out.println("Enter your percent: ");
float percent = sc.nextFloat();
System.out.println("Are you local (enter true or false): ");
boolean isLocal = sc.nextBoolean();
System.out.println("Enter your grade(enter A, or, B or, C or, D): ");
char grade = sc.next().toCharArray()[0];
Student std = new Student(name, age, percent, isLocal, grade);
std.displayDetails();
}
}输出结果
Enter your name: Krishna Enter your age: 25 Enter your percent: 86 Are you local (enter true or false): true Enter your grade(enter A, or, B or, C or, D): A Details.............. Name: Krishna Age: 25 Percent: 86.0 Nationality: Indian Grade: A
Java的BufferedReader类用于从指定的源读取字符流（字符输入流）。此类的构造函数接受InputStream对象作为参数，您可以传递InputStreamReader。
以下Java程序使用BufferedReader 类从用户读取数据。
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
class Student{
String name;
int age;
float percent;
boolean isLocal;
char grade;
Student(String name, int age, float percent, boolean isLocal, char grade){
this.name = name;
this.age = age;
this.percent = percent;
this.isLocal = isLocal;
this.grade = grade;
}
public void displayDetails(){
System.out.println("Details..............");
System.out.println("Name: "+this.name);
System.out.println("Age: "+this.age);
System.out.println("Percent: "+this.percent);
if(this.isLocal) {
System.out.println("Nationality: Indian");
}else {
System.out.println("Nationality: Foreigner");
}
System.out.println("Grade: "+this.grade);
}
}
public class ReadData {
public static void main(String args[]) throws IOException {
BufferedReader reader =new BufferedReader(new InputStreamReader(System.in));
System.out.println("Enter your name: ");
String name = reader.readLine();
System.out.println("Enter your age: ");
int age = Integer.parseInt(reader.readLine());
System.out.println("Enter your percent: ");
float percent = Float.parseFloat(reader.readLine());
System.out.println("Are you local (enter true or false): ");
boolean isLocal = Boolean.parseBoolean(reader.readLine());
System.out.println("Enter your grade(enter A, or, B or, C or, D): ");
char grade = (char) reader.read();
Student std = new Student(name, age, percent, isLocal, grade);
std.displayDetails();
}
}输出结果
Enter your name: Krishna Enter your age: 25 Enter your percent: 86 Are you local (enter true or false): true Enter your grade(enter A, or, B or, C or, D): A Details.............. Name: Krishna Age: 25 Percent: 86.0 Nationality: Indian Grade: A
此类用于从控制台（键盘/屏幕）设备写入/读取数据。它提供了readLine() 方法，该方法从键盘读取一行。您可以使用console()方法获取Console类的对象。
注意-如果您尝试在非交互式环境（例如IDE）中执行此程序，则该程序将无法正常工作。
以下Java程序使用Console 类从用户读取数据。
import java.io.BufferedReader;
import java.io.Console;
import java.io.IOException;
import java.io.InputStreamReader;
class Student{
String name;
int age;
float percent;
boolean isLocal;
char grade;
Student(String name, int age, float percent, boolean isLocal, char grade){
this.name = name;
this.age = age;
this.percent = percent;
this.isLocal = isLocal;
this.grade = grade;
}
public void displayDetails(){
System.out.println("Details..............");
System.out.println("Name: "+this.name);
System.out.println("Age: "+this.age);
System.out.println("Percent: "+this.percent);
if(this.isLocal) {
System.out.println("Nationality: Indian");
}else {
System.out.println("Nationality: Foreigner");
}
System.out.println("Grade: "+this.grade);
}
}
public class ReadData {
public static void main(String args[]) throws IOException {
Console console = System.console();
if (console == null) {
System.out.println("Console is not supported");
System.exit(1);
}
System.out.println("Enter your name: ");
String name = console.readLine();
System.out.println("Enter your age: ");
int age = Integer.parseInt(console.readLine());
System.out.println("Enter your percent: ");
float percent = Float.parseFloat(console.readLine());
System.out.println("Are you local (enter true or false): ");
boolean isLocal = Boolean.parseBoolean(console.readLine());
System.out.println("Enter your grade(enter A, or, B or, C or, D): ");
char grade = console.readLine().toCharArray()[0];
Student std = new Student(name, age, percent, isLocal, grade);
std.displayDetails();
}
}输出结果
Enter your name: Krishna Enter your age: 26 Enter your percent: 86 Are you local (enter true or false): true Enter your grade(enter A, or, B or, C or, D): A Details.............. Name: Krishna Age: 26 Percent: 86.0 Nationality: Indian Grade: A