基本语法

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Input/Output

Java, like all other languages, supports three standard input/output streams: System.in (standard input device), System.out (standard output device), and System.err (standard error device).

inout

import java.util.Scanner;    // Needed to use the Scanner for keyboard input

public class ScannerTest {
   public static void main(String[] args) {
      // Declare variables
      int num1;
      double num2;
      String str;

      Scanner in = new Scanner(System.in);
      num1 = in.nextInt();         // Use nextInt() to read an int
      num2 = in.nextDouble();      // Use nextDouble() to read a double
      str  = in.next();            // Use next() to read a String token, up to white space
      str = in.nextLine();         //read in the entire line
      in.close();   // Scanner not longer needed, close it

      // Formatted output via printf()
      System.out.printf("%s, Sum of %d & %.2f is %.2f%n", str, num1, num2, num1+num2);
   }
}

output

• System.out.println(*aString*) (print-line) prints *aString*, and advances the cursor to the beginning of the next line.
  • 换行
• System.out.print(*aString*) prints *aString* but places the cursor after the printed string.
  • 不换行
• printf: 格式化输出

System.out.print("GPA is"+gpa);

类型

final $\approx $ const