# 问题和练习

问题
练习

# 问题

1.使用 API 文档来查找以下问题的答案：

Integer 可以使用什么方法将 int 字符串转换为以十六进制表示数字的字符串？例如，什么方法将整数 65 转换为字符串 “41”？

答：
```
Integer.toHexString(16) // 10
Integer.toHexString(65) // 41
```
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Integer 会用什么方法将基数 5 中的字符串转换成等价的 int？例如，如何将字符串 “230” 转换为整数值 65？显示您将用于完成此任务的代码。

答：
```
valueOf. Heres how:

String base5String = "230";
int result = Integer.valueOf(base5String, 5);
```
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您可以使用 Double 什么方法来检测浮点数是否具有特殊值不是一个 NaN

答：
```
Double.isNaN(number)
```
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2.问题：下列表达式的值是什么？为什么？

Integer.valueOf(1).equals(Long.valueOf(1))

答：错。两个对象（Integer 和 Long）是不同的类型。

# 练习

1.把下列代码修改成打印最小值；并删除 aChar 和 aBoolean

public class MaxVariablesDemo {
    public static void main(String args[]) {

        //integers
        byte largestByte = Byte.MAX_VALUE;
        short largestShort = Short.MAX_VALUE;
        int largestInteger = Integer.MAX_VALUE;
        long largestLong = Long.MAX_VALUE;

        //real numbers
        float largestFloat = Float.MAX_VALUE;
        double largestDouble = Double.MAX_VALUE;

        //other primitive types
        char aChar = 'S';
        boolean aBoolean = true;

        //Display them all.
        System.out.println("The largest byte value is "
                                   + largestByte + ".");
        System.out.println("The largest short value is "
                                   + largestShort + ".");
        System.out.println("The largest integer value is "
                                   + largestInteger + ".");
        System.out.println("The largest long value is "
                                   + largestLong + ".");

        System.out.println("The largest float value is "
                                   + largestFloat + ".");
        System.out.println("The largest double value is "
                                   + largestDouble + ".");

        if (Character.isUpperCase(aChar)) {
            System.out.println("The character " + aChar
                                       + " is uppercase.");
        } else {
            System.out.println("The character " + aChar
                                       + " is lowercase.");
        }
        System.out.println("The value of aBoolean is "
                                   + aBoolean + ".");
    }
}

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答：


public class MinVariablesDemo {
    public static void main(String args[]) {

        // integers
        byte smallestByte = Byte.MIN_VALUE;
        short smallestShort = Short.MIN_VALUE;
        int smallestInteger = Integer.MIN_VALUE;
        long smallestLong = Long.MIN_VALUE;

        // real numbers
        float smallestFloat = Float.MIN_VALUE;
        double smallestDouble = Double.MIN_VALUE;

        // display them all
        System.out.println("The smallest byte value is " + smallestByte);
        System.out.println("The smallest short value is " + smallestShort);
        System.out.println("The smallest integer value is " + smallestInteger);
        System.out.println("The smallest long value is " + smallestLong);

        System.out.println("The smallest float value is " + smallestFloat);
        System.out.println("The smallest double value is " + smallestDouble);
    }
}

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剩下 2、3 题不想看了。官网传送门

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