java - 将 String 中提供的十进制数转换为二进制数

Question

我想将字符串格式的十进制数转换为二进制数。例如我想读取 2 并输出 10。

我尝试过:

Scanner input = new Scanner(System.in);
String dec;
dec = input.next();
int bin = Integer.parseInt(dec, 2);
System.out.println(bin);

输入 2 时出现以下错误:

Exception in thread "main" java.lang.NumberFormatException: For input string: "2" under radix 2
    at java.base/java.lang.NumberFormatException.forInputString(NumberFormatException.java:67)
    at java.base/java.lang.Integer.parseInt(Integer.java:665)
    at binarytest.BinaryTest.main(BinaryTest.java:23)

Answer 1

如commented by Ole V.V. ，从用户处获取一个int:

Scanner scanner = new Scanner( System.in );
int input = scanner.nextInt() ;

和convert to binary string .

String output = Integer.toBinaryString( input ) ;

引用another wise comment作者:Ole V.V.:

It’s a good exercise in distinguishing between a concept and its representation in the UI. Here the number is the concept. In the UI it’s represented either as a decimal number (on input) or a binary number (on output). Use an int for the concept of a number and forget whether it’s binary, decimal or something else, those are implementation details not relevant to the task at hand. And apply the proper conversions on input and output.