Java 类的数组';s对象和在foreach循环中访问
在这段代码中,我希望用户提供输入,但它正在生成Java 类的数组';s对象和在foreach循环中访问,java,class,foreach,Java,Class,Foreach,在这段代码中,我希望用户提供输入,但它正在生成 import java.util.Scanner; class A{ int age; public static void main(String[] args){ Scanner s=new Scanner(System.in); A[] a=new A[4]; System.out.println("Enter the elements:"); for(A i:a){ i.age=s.nex
import java.util.Scanner;
class A{
int age;
public static void main(String[] args){
Scanner s=new Scanner(System.in);
A[] a=new A[4];
System.out.println("Enter the elements:");
for(A i:a){
i.age=s.nextInt();
}
}
}
请告诉我这个错误。您已经初始化了数组,但是忘记初始化它的元素
Exception in thread "main" java.lang.NullPointerException
at A.main(a.java:10)
输出:
A[] a=new A[4];
for (int i = 0; i < a.length; i++) {
a[i] = new A();
}
A[] a = null;
// NO array object
System.out.println(Arrays.toString(a));
a = new A[4];
// Array object with NO elements
System.out.println(Arrays.toString(a));
for (int i = 0; i < a.length; i++) {
a[i] = new A();
}
// Array object with A() elements
System.out.println(Arrays.toString(a));
null
[null, null, null, null]
[A@15db9742, A@6d06d69c, A@7852e922, A@4e25154f]