急急急.......高精度减法出错java.lang.ArrayIndexOutOfBoundsException

[scauxie]

package cn.sub2.sub2;

import java.util.Scanner;

public class sub2 {
	public static void main(String[] args)

	{
		final int add1Max = 1000;// 可计算最长位数
		final int add2Max = 1000;

		int i, ka, kb;

		char[] a2 = new char[add1Max];
		char[] b2 = new char[add1Max];
		String a1;
		String b1;

		Scanner in = new Scanner(System.in);
		a1 = in.nextLine();// 输入高精度数；
		b1 = in.nextLine();
		ka = a1.length();// 获取长度；
		kb = b1.length();
		for (i = 0; i < a1.length(); i++)
			a2[i] = a1.charAt(i);// 将输入的高精度数，存入字符数组中；
		for (i = 0; i < b1.length(); i++)
			b2[i] = b1.charAt(i);

		int[] a = new int[ka];
		int[] b = new int[kb];
		for (i = 0; i < ka; i++)
			a[i] = a2[ka - i - 1] - '0';// 将字符数组中的元素变为整数存入整形数组；

		for (i = 0; i < kb; i++)
			b[i] = b2[kb - i - 1] - '0';

		int m = 0;
		for (i = a.length - 1; i >= 0; i--) {
			// 进行减法运算；
			m = a[i] - b[i];
			if (m < 0) {
				// 如果被减数的这一位小于减数；
				a[i] = m + 10;// 因为减得的是负数，所以加上10；
				a[i - 1] -= 1;// 再从前一位减一；
			} else
				a[i] = m;

		}
		for (i = ka - 1; i >= 0; i--)
			System.out.printf("%d", a[i]);

	}
}

[我是风]

for (i = a.length - 1; i >= 0; i--)
a[i - 1] -= 1;// 再从前一位减一；
数组越界

[li_d_s]

说了多少遍了，错误信息。。。。

[Inhibitory]

仔细理解编译器给出的错误信息的内容, 就是下标访问越界, 这种在数组中很常见, 要学会从编译器给出的错误信息去找到问题所在之处.

[anqini]

a[i - 1] -= 1;// 再从前一位减一；
这里越位了，当i为0的时候成了a[-1]1=1;

[kunlunningxue]

java.lang.ArrayIndexOutOfBoundsException
你的数组越界了！

[For_suzhen]

[Quote=引用 1 楼 powerlee2008 的回复:]
for (i = a.length - 1; i >= 0; i--)
a[i - 1] -= 1;// 再从前一位减一；
数组越界
[/Quote]
正解

[我是风]

给你个例子：

public class Sub2 {
	private String value;
	
	public Sub2(String minuend, String subtrahend) {
		this.subtract(minuend, subtrahend);
	}
	
	public String toString() {
		return this.value;
	}
	
	private boolean subtractIntStr(String minuend, String subtrahend, boolean isAppendZreo, boolean isBorrowed) {
		int loops = Math.max(minuend.length(), subtrahend.length());
		if(isAppendZreo) {
			for(int i = minuend.length(); i < loops; i++) {
				minuend += "0";
			}
			for(int i = subtrahend.length(); i < loops; i++) {
				subtrahend += "0";
			}
		} else {
			for(int i = minuend.length(); i < loops; i++) {
				minuend = "0" + minuend;
			}
			for(int i = subtrahend.length(); i < loops; i++) {
				subtrahend = "0" + subtrahend;
			}
		}
		int minuendBit;
		int subtrahendBit;
		for(int i = loops - 1; i >= 0; i--) {
			minuendBit = minuend.charAt(i) - 48;
			if(isBorrowed) {
				minuendBit--;
				isBorrowed = false;
			}
			subtrahendBit = subtrahend.charAt(i) - 48;
			if(minuendBit < subtrahendBit) {
				minuendBit += 10;
				isBorrowed = true;
			}
			this.value = Integer.toString(minuendBit - subtrahendBit) + this.value;
		}
		
		return isBorrowed;
	}
	
	private void subtract(String minuend, String subtrahend) {
		int index = minuend.indexOf('.');
		String minuendInteger = minuend;
		String minuendFract = "";
		if(index >= 0 && index < minuend.length()) {
			minuendInteger = minuend.substring(0, index);
			minuendFract = minuend.substring(index + 1);
		}
		index = subtrahend.indexOf('.');
		String subtrahendInteger = subtrahend;
		String subtrahendFract = "";
		if(index >= 0 && index < subtrahend.length()) {
			subtrahendInteger = subtrahend.substring(0, index);
			subtrahendFract = subtrahend.substring(index + 1);
		}
		this.value = "";
		boolean isBorrowed = this.subtractIntStr(minuendFract, subtrahendFract, true, false);
		this.value = "." + this.value;
		isBorrowed = this.subtractIntStr(minuendInteger, subtrahendInteger, false, isBorrowed);
		
		while(this.value.length() > 1) {
			if(this.value.charAt(0) == '0') {
				if(this.value.charAt(1) == '.') {
					break;
				}
				this.value = this.value.substring(1);
			} else {
				break;
			}
		}
		
		if(isBorrowed) {
			String newMinuend  = "1";
			index = this.value.indexOf('.');
			if(!(index >= 0 && index < this.value.length())) {
				index = this.value.length();
			}
			for(int i = 0; i < index; i++) {
				newMinuend += "0";
			}

			String newSubtrahend = new String(this.value);
			this.value = "";
			this.subtract(newMinuend, newSubtrahend);
			this.value = "-" + this.value;
		}
		int lastIndex = this.value.length() - 1;
		if(this.value.charAt(lastIndex) == '.') {
			this.value = this.value.substring(0, lastIndex);
		}
	}
	
	public static void main(String[] args) {
		Sub2 sub2 = new Sub2("10.00", "1234567890123456789012345678901234567890.123456789");
		System.out.println(sub2.toString());
	}
}

[richard_2010]

错误信息是下标访问越界的意思，哪里越界了，见上面的提示

[scauxie]

那要怎么改正哦，可不可以教一下？7楼的代码没有注释，有些地方看不明。我把里面的main()改成

       public static void main(String[] args) {
    	Scanner in=new Scanner(System.in);
        //Sub2 sub2 = new Sub2("1000325123512351515", "1223512532523512352151533335234325312513");
        String a=new String();
        String b=new String();
         a=in.nextLine();
         b=in.nextLine();
        Sub2 sub2 = new Sub2(a,b);
        System.out.println(sub2.toString());
    }

得到的结果不正确，疑惑ing...

[我是风]

public static void main(String[] args) {
	Scanner in = new Scanner(System.in);
	String a = in.nextLine();
	String b = in.nextLine();
	Sub2 sub2 = new Sub2(a, b);
	System.out.println(sub2.toString());
}

没错阿

[scauxie]

咦？可以了，谢谢！！！