Java 例外，需要了解什么是错误的？

{

}

我的错误是：

线程主java.lang.StringIndexOutOfBoundsException中的异常： 字符串索引超出范围：0处 java.lang.String.charAtString.java:658 at lab1.lab01.mainlab01.java:42

到底出了什么问题？

虽然字符串不像在C中那样完全是char[]，但对于某些操作，最好将其视为一个

当您尝试索引到一个空的或未初始化的数组时，您将得到一个类似的异常-ArrayIndexOutOfBoundsException。这意味着您正试图索引到不存在的内容

我们知道大小为N的数组可以索引到位置N-1。对于N=0，我们将通过数学方法索引到位置-1

当你表演角色扮演时，同样的事情也会发生。您正在尝试检索一个不存在的值。换句话说：您的字符串是空的

罪魁祸首是这样的：

private static final int StringIndexOutOfBoundsException = 0;
//values shared within the class
private static int sideA = 0;
private static int sideB = 0;


//main method
public static void main(String [] args)


{

System.out.println("Usage: Supply 2 integer values as triangle sides."); 
System.out.println("    A-integer value");
System.out.println("    B-integer value");
System.out.println("    C-attempt a pythagorean calculation");
System.out.println("    Q-quit the program");


String value = null;
String side;
char c = 0;

int s1 =StringIndexOutOfBoundsException;

Scanner scanner = new Scanner(System.in);
boolean carryOn=true;
while(carryOn)                //loop until user has finished.
{
    side = JOptionPane.showInputDialog(null, "A or B?");
try
{
    c =side.charAt(0);
} catch(NullPointerException NP){
    System.out.println("Thanks you are done!");
}


    switch(c)                 //which side is the user trying to set
    {
    case 'Q':
        carryOn= false; //quit the program
        break;

    case 'A':
        try{
        value = JOptionPane.showInputDialog(null, "Enter A"); 
        sideA = Integer.parseInt(value);
        } catch(NumberFormatException NF){
            System.out.println("Thats not a number. Type in an integer.");
            break;
        }
        if (sideA<=0)
        {
        System.out.println("Cannot compute because A is zero. Try another integer");
        break;
        }
        if(sideA>0)
        {
            System.out.println("You've inputed an A value. That value is "+sideA);
            break;
        }

        break;

    case 'B':
            try{
            value = JOptionPane.showInputDialog(null, "Enter B"); 
            sideB = Integer.parseInt(value);
            } catch(NumberFormatException NF){
                System.out.println("Thats not a number. Type in an integer.");
                break;
            }
            if (sideB<=0)
            {
                System.out.println("Cannot compute because B is zero. Try another integer");
                break;
                }
            if(sideB>0)
            {
                System.out.println("You've inputed an B value. That value is "+sideB);
                break;
            }


            break;

    case 'C':          //calculate an answer
        double temporary = (sideA * sideA) + (sideB * sideB);
        if(sideA <=0 && sideB <=0){
            System.out.println("You don't have triangle. Try again");
            break;
        }
        double result = java.lang.Math.sqrt(temporary);
        System.out.println("The hypotenuse value is "+result);
        break;
    }



    }
System.out.println("Thank you. Goodbye!");
return;

    }

c =side.charAt(0);

若边是空的，你们就卡住了

当您转到检索side的值时，如此行所示：

private static final int StringIndexOutOfBoundsException = 0;
//values shared within the class
private static int sideA = 0;
private static int sideB = 0;


//main method
public static void main(String [] args)


{

System.out.println("Usage: Supply 2 integer values as triangle sides."); 
System.out.println("    A-integer value");
System.out.println("    B-integer value");
System.out.println("    C-attempt a pythagorean calculation");
System.out.println("    Q-quit the program");


String value = null;
String side;
char c = 0;

int s1 =StringIndexOutOfBoundsException;

Scanner scanner = new Scanner(System.in);
boolean carryOn=true;
while(carryOn)                //loop until user has finished.
{
    side = JOptionPane.showInputDialog(null, "A or B?");
try
{
    c =side.charAt(0);
} catch(NullPointerException NP){
    System.out.println("Thanks you are done!");
}


    switch(c)                 //which side is the user trying to set
    {
    case 'Q':
        carryOn= false; //quit the program
        break;

    case 'A':
        try{
        value = JOptionPane.showInputDialog(null, "Enter A"); 
        sideA = Integer.parseInt(value);
        } catch(NumberFormatException NF){
            System.out.println("Thats not a number. Type in an integer.");
            break;
        }
        if (sideA<=0)
        {
        System.out.println("Cannot compute because A is zero. Try another integer");
        break;
        }
        if(sideA>0)
        {
            System.out.println("You've inputed an A value. That value is "+sideA);
            break;
        }

        break;

    case 'B':
            try{
            value = JOptionPane.showInputDialog(null, "Enter B"); 
            sideB = Integer.parseInt(value);
            } catch(NumberFormatException NF){
                System.out.println("Thats not a number. Type in an integer.");
                break;
            }
            if (sideB<=0)
            {
                System.out.println("Cannot compute because B is zero. Try another integer");
                break;
                }
            if(sideB>0)
            {
                System.out.println("You've inputed an B value. That value is "+sideB);
                break;
            }


            break;

    case 'C':          //calculate an answer
        double temporary = (sideA * sideA) + (sideB * sideB);
        if(sideA <=0 && sideB <=0){
            System.out.println("You don't have triangle. Try again");
            break;
        }
        double result = java.lang.Math.sqrt(temporary);
        System.out.println("The hypotenuse value is "+result);
        break;
    }



    }
System.out.println("Thank you. Goodbye!");
return;

    }

c =side.charAt(0);

…添加一个检查以确保它不是空的，并等待获得有效的长度

side = JOptionPane.showInputDialog(null, "A or B?");

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你试过使用调试器吗？你看过第42行了吗？它正盯着你看。读取异常名称。转到指示的行。解决问题。信息能比现在更清晰吗？？？