多项式添加:无法运行代码
多项式添加:无法运行代码
提问于 2015-04-27 17:52:21
这个程序在Eclipse上。我必须声明变量"Integer“而不是"int”。在编译时，此代码没有显示错误，但存在运行时错误。请解决这个问题。
运行时错误：
Exception in thread "main" java.lang.NullPointerException
at Polynomial.add(Polynomial.java:17)
at PolynomialTest.main(PolynomialTest.java:7)Polynomial.java
public class Polynomial{
Integer coef[];
Integer exp;
public Polynomial(Integer a, Integer b) {
coef = new Integer[b+1];
coef[b] = a;
exp = b;
}
// return c = a + b
public Polynomial add(Polynomial b) {
Polynomial a = this;
Polynomial c= new Polynomial(0, Math.max(a.exp, b.exp));
for (Integer i = 0; i <= a.exp; i++){
c.coef[i] = c.coef[i] + a.coef[i];
}
for (int i = 0; i <= b.exp; i++){
c.coef[i] += b.coef[i];
}
return c;
}
public String toString() {
if (exp == 0){
return "" + coef[0];
}else
if (exp == 1){
return coef[1] + "x + " + coef[0];
}
String s = coef[exp] + "x^" + exp;
for (int i = exp-1; i >= 0; i--) {
if (coef[i] == 0){
continue;
}
else if (coef[i] > 0){
s = s + " + " + ( coef[i]);
}
if (i == 1){
s = s + "x";
}
else
if (i > 1) {
s = s + "x^" + i;
}
}
return s;
}}PolynomialTest.java
public class PolynomialTest {
// test client
public static void main(String[] args) {
Polynomial p1 = new Polynomial(4, 4);
Polynomial p2 = new Polynomial(7, 2);
Polynomial p3 = new Polynomial(3, 0);
Polynomial p = p1.add(p2).add(p3); // 4x^3 + 3x^2 + 1
Polynomial q1 = new Polynomial(2, 2);
Polynomial q2 = new Polynomial(5, 4);
Polynomial q = q1.add(q2);
System.out.println("p(x) = " + p);
System.out.println("q(x) = " + q);
System.out.println("p(x) + q(x) = " + p.add(q));
}
}回答 1
Stack Overflow用户
回答已采纳
发布于 2015-04-27 18:30:05
由于Integer是一个对象，因此需要使用新的Integer对象初始化coef数组中的每个条目。
您可以在Polynomial构造函数中这样做：
public class Polynomial{
Integer coef[];
Integer exp;
public Polynomial(Integer a, Integer b) {
coef = new Integer[b+1];
for (int i = 0; i < coef.length; i++){
coef[i] = new Integer(0); //create a new Integer and initialize to zero
}
coef[b] = a;
exp = b;
}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/29902693
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