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我有类A和B,我要访问从A类的方法在B类,但它不工作,我得到了以下信息:的Java访问方法
异常在线程“主要”显示java.lang.NullPointerException
,是造成这种情况的特定部分被访问时ba
:
ba.getBalance() >= LIM
ba.debit(LIM);
我不知道我是d因为我创建了私有字段并在main中初始化了它。乙
类:
public class B {
private A ba;
private long balance;
public B(long amount, A ba){
}
public boolean testCase(long amount){
//..
}
public long getBalance(){
return balance;
}
A类:
public class A {
private long balance;
public A(long amount){
}
public boolean debit(long amount){
//.. simple arithmetic
}
public long getBalance(){
return balance;
}
主要
A aa = new BankAccount(amount1); // where amounts are user input
B bb = new GoCardAccount(amount2, aa);
您需要将传递给'B'构造函数的'ba'实例分配给您的专用成员'ba',就像您为'amount'所做的那样: 'public B(long amount,A ba){this.ba = ba; this.balance = amount}' –