小编Doe*_*ter的帖子

我正在尝试解决一个基本功能.但是我的第二个if语句和else会出错.如果你能在这里给我一个帮助,那就是代码.

(define (equation x)
  (if(> x 2) (+(-(* x x) x) 4) ) 
  (if (and (> x 1 ) (= x 1))  (and (< x 2) (= x 2)) (/ 1 x))
  (else 0)
  )

我的两个密码验证方法有问题.方法hasDigitsAndLetters应该检查字符串的所有字符是否是数字和字母,第二种方法hasTwoDigits应该检查传递中是否至少有两位数,但问题是对于预期的结果是真的它们是ruturning假.如果有人可以帮忙.这是代码.

//check if the whole string consists of digits and letters
    public static boolean hasDigitsAndLetters(String pass)
    {
        for(int i=0; i<pass.length(); i++)
        {
            if(!Character.isLetterOrDigit((i)))
            {
                return false;
            }

        }
        return true;
    }



    // check whether the password has at least 2 digits
    public static boolean hasTwoDigits(String pass)
    {
        int counter = 0;
        for(int i=0; i<pass.length(); i++)
        {
            if(Character.isDigit(i))
            {
                counter ++;
            }

        }
        System.out.println("Number of digits: " + counter);
        if(counter >= 2)
        {
            return true;
        }
        return false;
    }

我试图实现一个简单的树形图来计算整数的出现,但它给了我一个NullPointerException,我不知道如何解决它.

Exception in thread "main" java.lang.NullPointerException
    at exercises.CountOccurances_20_07.main(CountOccurances_20_07.java:21)

这是代码:

import java.util.Map;
import java.util.Set;
import java.util.TreeMap;

public class CountOccurances_20_07 
{
    public static void main(String[] args) 
    {
        int[] list = {2, 3, 40, 3, 5, 4, 3, 3, 3, 2, 0};
        Map<Integer, Integer> map = new TreeMap<Integer, Integer>();
        for(int i: list)
        {
            int key = list[i];
            if(list.length > 1)
            {
                if(map.get(key) == 0)
                {
                    map.put(key, 1);
                }
                else
                {
                    int value = map.get(key).intValue(); // line 21
                    value ++;
                    map.put(key, value); …

当我为月利率和1年投资金额4.25输入1000时,为什么我得到的结果是4.384414858452464E11而不是预期的1043.34？

import java.util.Scanner;

public class FinancialApplicationFutureInvestment_13 {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.println("Enter investment amount: ");
        int investmentAmount = input.nextInt();
        System.out.println("Enter monthly interest rate: ");
        double monthlyInterestRate = input.nextDouble();
        System.out.println("Enter number of years");
        int numOfYears = input.nextInt();

        double futureInvestmentValue = investmentAmount *
            (Math.pow(1 + monthlyInterestRate, numOfYears * 12));
        System.out.println("Accumulated value is: " + futureInvestmentValue);

        double test = Math.pow(1 + monthlyInterestRate, numOfYears * 12);
        System.out.println(test);
    }
}

我试图在框架中显示一个简单的jtable,但它没有显示表的列,我跟着oracle教程中的示例,但有一些我做得不对.该程序正在编译和运行.这是代码:

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTable;

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.math.BigDecimal;
import java.math.RoundingMode;

public class SimpleTableDemo extends JPanel 
{

    SimpleTableDemo()
    {
        String[] columnNames = {"#",
                "Repayment Dates",
                "Principle Amount",
                "Interest",
                "Comission fee",
                "Total installement amount", 
                "Principle balance"};

//      BigDecimal bd = new BigDecimal(d).setScale(2, RoundingMode.HALF_EVEN);
        //each line of the two dimentional array is a line in the table
        Object[][] data = {
                {new Integer(1), new java.util.Date(), new BigDecimal(12509.23).setScale(2, RoundingMode.HALF_EVEN), new BigDecimal(1571.77).setScale(2, …

我正在尝试实现责任链模式,但似乎我缺少一些东西,因为在具体的类中,setnexthandler没有设置下一个但总是相同的.我想我的错误是在else statems next.setNextHandler(next)中的processMalfunction()方法的具体类中; 我认为它应该是next.setNextHandler(Severity.Medium)的第一个.所以这是代码,如果你可以看看.这是代码.

public interface MalfunctionHandler 
{
    public void processMalfunction(Malfunction malfunciton);
    public void setNextHandler(MalfunctionHandler handler);
}

public enum Severity 
{
    TRIVIAL, LOW, MEDIUM, HIGH
}

public class Malfunction
{
    /**
     * severity is a type of Severity 
     */
    Severity severity;

    /**
     * @param description describes the severity of the problem
     */
    String description;

    Malfunction(Severity severity, String description)
    {
        if(description == null)
        {
            description = "No description available. Probably serious.";
        }

        if(description.isEmpty())
        {
            description = "No description available. Probably serious."; …

我已经推出了一个Arraylist,我希望它是一个泛型类型.

ArrayList<T> locker = new ArrayList<T>();

然后我有一个方法添加,也需要是通用的.

public <T extends Gear> boolean add(Gear item)
{

    locker.add(item);// this is giving me compile error => no suitable method found for add(Gear)
    return true;
}

我该如何修复它,我也是通用类型的新手.

我试图实现冒泡排序,但我不确定它是否正确.如果你可以看看它是否是一个泡沫排序,可以更好地完成,请不要害羞.这是代码:

package Exercises;

import java.util.*;

public class BubbleSort_6_18 
{
    public static void main(String[] args) 
    {
        Random generator = new Random();

        int[] list = new int[11];
        for(int i=0; i<list.length; i++)
        {
            list[i] = generator.nextInt(10);
        }

        System.out.println("Original Random array: ");
        printArray(list);

        bubbleSort(list);

        System.out.println("\nAfter bubble sort: ");
        printArray(list);
    }

    public static void bubbleSort(int[] list)
    {
        for(int i=0; i<list.length; i++)
        {
            for(int j=i + 1; j<list.length; j++)
            {
                if(list[i] > list[j])
                {
                    int temp = list[i];
                    list[i] = list[j];
                    list[j] = temp;
                }
            } …

大家好,我真的被卡住,我一直在接受java.lang.NullPointerException.我试图在每个可能的地方处理它,但我没有成功地做到这一点.这是家庭作业.如果你能看一下并给出一些关于java.lang.NullPointerException它的反馈,那就太好了.异常发生在Captain.handleProblem() 和MalfucntionHandler.proccessMalfunction()

    public abstract class MalfunctionHandler 
    {

        MalfunctionHandler next;
        /**
         * severity is a type of Severity 
         */
        Severity severity;

        /**
         * @param description describes the severity of the problem
         */
        String description;


        /**
         * @param f file object  that refers to the log-silver.txt
         */
        File f = new File("log-silver.txt");

        MalfunctionHandler(Severity severity)
        {
                this.severity = severity;
        }
         public String getDescription()
        {
            if(description == null)
            {
                description = "No description available. Probably serious.";
            }
            return …