这个程序在Eclipse上。我必须声明变量"整数"不是" int"。当我编译时,此代码显示没有错误,但存在运行时错误。请解决此问题。
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));
}
}
答案 0 :(得分:0)
由于Integer
是一个对象,因此您需要使用新的coef
对象初始化Integer
数组中的每个条目。
您可以在Polynomial
构造函数中执行此操作:
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;
}