Java查源碼方法

在學習迭代器的過程中，想看iterator的hasNext（）和next（）的源碼實現，可用getClass找到源碼位置 

import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;

public class test {
    public static void main(String[] args) {
        Collection<Integer> collection = new ArrayList();
        collection.add(123);
        collection.add(234);
        collection.add(345);
        Iterator<Integer> it = collection.iterator();
        while(it.hasNext()){
            System.out.println(it.next());
        }
        MyGenericMethod mg = new MyGenericMethod();
        mg.show(123);
        mg.show(it);   // 找源碼方法 getClass()

    }

}

class MyGenericMethod{
    public <MVP> void show(MVP mvp){
        System.out.println(mvp.getClass());
    }
}

輸出如下：

123
234
345
class java.lang.Integer
class java.util.ArrayList$Itr

 

附上Itr類代碼：

private class Itr implements Iterator<E> {
    int cursor;       // index of next element to return
    int lastRet = -1; // index of last element returned; -1 if no such
    int expectedModCount = modCount;

    public boolean hasNext() {
        return cursor != size;
    }

    @SuppressWarnings("unchecked")
    public E next() {
        checkForComodification();
        int i = cursor;
        if (i >= size)
            throw new NoSuchElementException();
        Object[] elementData = ArrayList.this.elementData;
        if (i >= elementData.length)
            throw new ConcurrentModificationException();
        cursor = i + 1;
        return (E) elementData[lastRet = i];
    }

    public void remove() {
        if (lastRet < 0)
            throw new IllegalStateException();
        checkForComodification();

        try {
            ArrayList.this.remove(lastRet);
            cursor = lastRet;
            lastRet = -1;
            expectedModCount = modCount;
        } catch (IndexOutOfBoundsException ex) {
            throw new ConcurrentModificationException();
        }
    }

    @Override
    @SuppressWarnings("unchecked")
    public void forEachRemaining(Consumer<? super E> consumer) {
        Objects.requireNonNull(consumer);
        final int size = ArrayList.this.size;
        int i = cursor;
        if (i >= size) {
            return;
        }
        final Object[] elementData = ArrayList.this.elementData;
        if (i >= elementData.length) {
            throw new ConcurrentModificationException();
        }
        while (i != size && modCount == expectedModCount) {
            consumer.accept((E) elementData[i++]);
        }
        // update once at end of iteration to reduce heap write traffic
        cursor = i;
        lastRet = i - 1;
        checkForComodification();
    }

    final void checkForComodification() {
        if (modCount != expectedModCount)
            throw new ConcurrentModificationException();
    }
}