The iterator mode provides a unified interface for traversing the collection elements, using a consistent method to traverse the collection elements, without knowing the underlying representation of the collection object, that is: not exposing its internal structure
The role of
the type of hidden
inner class can access unlimited external members of its class, including private members
/*
*Inner class (inner class)
*Definition: the class defined in the class, method body, interface
*Function
*Used for type hiding
*Inner class has unlimited access to the members of its outer class, including private members
*/
/*Iterator mode (iterator): abstraction of access actions
- A collection of data stored at the bottom: an array (int), private, not directly accessible by the outside world
- Implement iterators through private inner classes
- Named inner class
- Anonymous inner class
*/
//迭代器接口
public interface Iterator {
int current();
int next();
boolean isFinish();
}
public class Sequence {
private int[] data;
private int cur;
public Sequence(int n) {
data = new int[n];
for (int k = 1; k <= n; k++) data[k-1] = k;
}
//返回一个接口，让外界按指定的顺序读取data
public Iterator iterator() {
cur = 0;
return new NormalIterator();
}
//顺序访问，类型隐藏，DAO
private class NormalIterator implements Iterator {
@Override
public int current() {
return data[cur];
}
@Override
public int next() {
if (cur < data.length) cur++;
if (isFinish()) return -1;
return data[cur];
}
@Override
public boolean isFinish() {
return (cur == data.length);
}
}
//逆序访问，在方法中定义的匿名内部类
public Iterator invIterator() {
cur = data.length - 1;
//改为用在方法中定义的匿名内部类实现
return new Iterator() {
@Override
public int current() {
return data[cur];
}
@Override
public int next() {
if (cur >=0) cur--;
if (isFinish()) return -1;
return data[cur];
}
@Override
public boolean isFinish() {
return (cur == -1);
}
};
}
}
public static void main(String[] args) {
Sequence s = new Sequence(20);
//Iterator iter = s.iterator();
Iterator iter = s.invIterator();
do {
System.out.print(iter.current() + " ");
iter.next();
} while (!iter.isFinish());
}