Question

需要一些帮助来弄清楚为什么我的代码的最后一部分会出错。谁能告诉我什么是错的？我正在使用NetBeans进行一个介绍级别的编程类，并且无法弄清楚为什么这是错误的。

我收到以下错误：

找不到符号符号：变量rat04位置：类Rational

package rational;

import java.util.logging.Level;
import java.util.logging.Logger;

public class Rational {
    // the numer and denom fields represent a fraction
    // CLASS INVARIANTS:
    // CI1: denom is not 0,
    // CI2: denom is positive,
    // CI3: numer and denom are in lowest terms.
    private final int numer;
    private final int denom;

    //toString and toDouble
    public String toString() {
        return numer + "/" + denom;
    }

    public double toDouble() {
        return 1.0 * numer / denom;
    }

    //utility method
    private static int greatestCommonDivisor(int a, int b) {
        int c;
        while (b != 0) {
            c = a % b;
            a = b;
            b = c;
        }
        return Math.abs(a);
    }

    private static void testGcd() {
        System.out.println("");
        System.out.println("Test Greatest Common Denominator");
        System.out.println("");
        for (int i = -21; i < 31; i += 2) {
            for (int j = -17; j < 31; j += 3) {
                System.out.printf("\n%5d%5d%5d", i, j, greatestCommonDivisor(i, j));
            }
        }
        System.out.println("");
    }

    public Rational(int numer, int denom) throws ZeroDenomException {
        // CI1. No way to fix, must throw exception.
        if (denom == 0) {
            throw new ZeroDenomException();
        }
        // CI2. Can fix.
        if (denom < 0) {
            numer *= -1;
            denom *= -1;
        }
        // CI3. Can fix.
        int gcd = greatestCommonDivisor(numer, denom);
        if (gcd != 1) {
            numer /= gcd;
            denom /= gcd;
        }
        // all class invariants now satisfied, initialize fields:
        this.numer = numer;
        this.denom = denom;
    }

    public Rational(int book) throws ZeroDenomException {
        //this(integer, 1);
        //this(1, book);
        this(book, 1);
    }

    public Rational() throws ZeroDenomException {
        this(0);
    }

    private static void testClass() throws ZeroDenomException {
        System.out.println("Rational tests.");
        System.out.println("");

        System.out.println("Test C-tor");
        System.out.println("Expected outcome: 4/25, -4/25, -4/25," + "4/25 17/1, 0/1.");
        System.out.println("");
        Rational rat01 = new Rational(144, 900);
        Rational rat02 = new Rational(-144, 900);
        Rational rat03 = new Rational(144, -900);
        Rational rat04 = new Rational(-144, -900);
        Rational rat05 = new Rational(17);
        Rational rat06 = new Rational();
        System.out.println("rat01 = " + rat01);
        System.out.println("rat02 = " + rat02);
        System.out.println("rat03 = " + rat03);
        System.out.println("rat04 = " + rat04);
        System.out.println("rat05 = " + rat05);
        System.out.println("rat06 = " + rat06);
    }

    public static void main(String[] args) {
        System.out.println("Rational class");
        System.out.println("Implemented by (My Name)");
        try {
            testClass();
            //testGcd();  
        } catch (ZeroDenomException ex) {
            System.out.println("Zero demon exception in testClass()! (J:H)");
        }

        System.out.println("");
        System.out.println("Try bad input");
        try {
            Rational rat00 = new Rational(0, 0);
        } catch (ZeroDenomException zde) {
            System.out.println(" Expected Zero Denominator Exception. " + zde);
        } catch (Exception e) {
            System.out.println("Should not be a general Exception.");
        }
        System.out.println("");

        System.out.println("");
        System.out.println("Test toDouble. Expect 0.16");
        System.out.println("rat04 to double: " + rat04.toDouble());
    }
}

Answer 1

您在rat04中声明testClass并在main中使用它。范围不同。

您不能使用从一个范围到另一个范围的变量。

您可以在类（成员变量）中创建一个静态变量，以便在需要时可以从两种方法访问（但实际上不应该......）

public class Rational {
    static Rational rat04;
    ...
}

或者只是不打印main中的值，而是打印在testClass所属的值中。

无法找出作业开始程序员

1 个答案: