public class Object {
    private static native void registerNatives();
    // 声明后有紧接静态代码块
    static {
        registerNatives();
    }
}

public static void main(String[] args) {
    int i = 0;
    Integer j = new Integer(0);
    System.out.println(j == i);
    System.out.println(j.equals(i));
}

true
true

Connection con = DriverManager.getConnection(url, username, password);
Statement sta = con.createStatement();
String sql = "select * from student";
ResultSet resultSet = sta.executeQuery(sql);

int sum = 0;      
while(resultSet.next()){      
    sum++;      
}

public class Singleton(){
	private static class Inner {
		private static Singleton instance = new Singleton();
	}
	private Singleton() {
	}
	public static Singleton getInstance(){
		return Inner.instance;
	}
}

final Button button = (Button) findViewById(R.id.button_id);
button.setOnClickListener(new View.OnClickListener() {
    public void onClick(View v) {
        // Perform action on click
    }
});

public void randomCards() {
	int[] data = new int[52];
	Random random= new Random();
	for (int i = 0; i < data.length; i++)
		data[i] = i;
	for (int i = data.length - 1; i > 0; i--) {
		int temp = random.nextInt(i+1); //产生 [0,i] 之间的随机数
		swap(data,i,temp);
	}
}

TomChens-MBP:util tomchen$ pwd
/Users/tomchen/Documents/javaEclipse/workspaceJava/OnlineOJ/src/util
TomChens-MBP:util tomchen$ ls
Main.java
TomChens-MBP:util tomchen$ cat Main.java 
package util; //包名
public class Main {
	public static void main(String[] args) {
		String s = "a" + "b" + "c" + "d";
		System.out.println(s);
	}
}

TomChens-MBP:util tomchen$ pwd
/Users/tomchen/Documents/javaEclipse/workspaceJava/OnlineOJ/src/util
TomChens-MBP:util tomchen$ java Main
Exception in thread "main" java.lang.NoClassDefFoundError: Main (wrong name: util/Main)
	at java.lang.ClassLoader.defineClass1(Native Method)
	at java.lang.ClassLoader.defineClass(ClassLoader.java:791)
	at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
	at java.net.URLClassLoader.defineClass(URLClassLoader.java:449)
	at java.net.URLClassLoader.access$100(URLClassLoader.java:71)
	at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
	at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:423)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:356)
	at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:482)

public static void bubbleSort(int[] arr, int size) {
	boolean swap = false;
	for (int i = 0; i < size - 1; i++) { //最多进行 n-1 趟
		swap = false;
		for (int j = size - 1; j > i; j--) { //从下往上扫描
			if (arr[j] < arr[j - 1]) {
				swap(arr, j, j - 1);
				swap = true;
			}
		}
		if (!swap) {
			break; // 未发生交换，终止算法
		}
	}
}

public static void swap(int[] arr, int one, int two) {
	int temp = arr[one];
	arr[one] = arr[two];
	arr[two] = temp;
}

// 排序范围 [start, end], 包含 end 
public static void quickSort(int[] arr, int start, int end) {
	if (start < end) {
		int p = partition(arr, start, end);
		quickSort(arr, start, p - 1);
		quickSort(arr, p + 1, end);
	}
}
// 一次划分代码，返回被划分后的基准位置
public static int partition(int[] arr, int left, int right) {
	int pivot = arr[left];
	while (left < right) {
		while (left < right && arr[right] >= pivot)
			right--;
		if (left < right)
			arr[left++] = arr[right];
		while (left < right && arr[left] <= pivot)
			left++;
		if (left < right)
			arr[right--] = arr[left];
	}
	arr[left] = pivot;
	return left;
}

public static void quickSort(int[] arr, int start, int end) {
	int[] stack = new int[end - start + 1]; // 数组模拟栈
	int len = 0;
	stack[len++] = start; // 入栈
	stack[len++] = end;
	while (len > 0) { // 栈中还有元素
		int right = stack[--len]; // 注意是 --len
		int left = stack[--len];
		int p = partition(arr, left, right);
		if (p - 1 > left) {
			stack[len++] = left;
			stack[len++] = p - 1;
		}
		if (p + 1 < right) {
			stack[len++] = p + 1;
			stack[len++] = right;
		}
	}
}

public static void insertSort(int[] arr, int size) {
	int temp = arr[0];
	for (int i = 1; i < size; i++) {
		// 若 arr[i] 不小于有序区的最后一个元素，直接扩大有序区
		if (arr[i] < arr[i - 1]) { 
			temp = arr[i];
			int j = i - 1;
			while (j >= 0 && temp < arr[j]) {
				arr[j + 1] = arr[j--];
			}
			arr[j + 1] = temp;
		}
	}
}

int[] a1 = { 1, 2, 3 }; //Java 风格
int a1[] = { 1, 2, 3 }; //C语言风格

int[] a2 = new int[] { 1, 2, 3 };
int a3[] = new int[] { 1, 2, 3 };
int[] a4 = new int[3];
for (int i = 0; i< a4.length; i++) 
	a4[i] = i;

for(int element: a4) 
	System.out.println(element);

0
1
2

public static void main(String[] args) {
	// testArr(a4); // 传入数组的引用，正确
	
	testArr(new int[] { 1, 2, 3 });
	// compile error
	// testArr({ 1, 2, 3 });
	// compile error
	// testArr(1, 2, 3);
}
public static void testArr(int[] nums) {
	for (int element : nums)
		System.out.println(element);
}

1
2
3

public static void testVariPara(int... nums) {
	for (int element : nums)
		System.out.println(element);
}

testVariPara(new int[] { 1, 2, 3 });
testVariPara(1, 2, 3);

System.out.println(a1.toString());

[I@182da3d

System.out.println(Arrays.toString(a1));

[1, 2, 3]

int[] arr = {1,2,3,4,5};
 
int[] copied = Arrays.copyOf(arr, 10); //10 是数组的长度
System.out.println(Arrays.toString(copied));
 
copied = Arrays.copyOf(arr, 3);
System.out.println(Arrays.toString(copied));

[1, 2, 3, 4, 5, 0, 0, 0, 0, 0]
[1, 2, 3]

int[] arr = {1,2,3,4,5};
 
int[] copied = new int[10];
System.arraycopy(arr, 0, copied, 1, 5);// 5是需复制的元素个数
 
System.out.println(Arrays.toString(copied));

[0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
[0, 1, 2, 3, 4, 5, 0, 0, 0, 0]

public static int[] copyOf(int[] original, int newLength) { 
   int[] copy = new int[newLength]; 
   System.arraycopy(original, 0, copy, 0, Math.min(original.length, newLength)); 
   return copy; 
}

int[] a1 = { 1, 2, 3 }; 
List<int[]> list = Arrays.asList(a1); // eclipse 提示修改为这样可以编译通过

List<Object> objList = Arrays.asList(obj1, obj2, obj3);

List<Object> objList = Arrays.asList(obj1);

List<Integer> exampleList = Arrays.asList(ArrayUtils.toObject(array));

Integer[] a1 = { 1, 2, 3 }; 
List<Integer> list = Arrays.asList(a1);
System.out.println(list);

List<Integer> list = Arrays.asList(1, 2, 3);
System.out.println(list);

List<Integer> list = Arrays.asList(1, 2, 3);
list.add(44); // 抛出 UnsupportedOperationException

// Arrays.ArrayList 源码
private static class ArrayList<E> extends AbstractList<E> {
    public E get(int index) {
        return a[index];
    }
    public E set(int index, E element) {
        E oldValue = a[index];
        a[index] = element;
        return oldValue;
    }
    public int indexOf(Object o) {
        if (o==null) {
            for (int i=0; i<a.length; i++)
                if (a[i]==null)
                    return i;
        } else {
            for (int i=0; i<a.length; i++)
                if (o.equals(a[i]))
                    return i;
        }
        return -1;
    }
    public boolean contains(Object o) {
        return indexOf(o) != -1;
    }
}

// AbstractList 源码
public abstract class AbstractList<E> extends AbstractCollection<E> implements List<E> {
    public void add(int index, E element) {
        throw new UnsupportedOperationException();
    }
    public E remove(int index) {
        throw new UnsupportedOperationException();
    }
}

ArrayList<Integer> list = new ArrayList<Integer>(Arrays.asList(1, 2, 3));

List<Integer> list = new ArrayList<>(Arrays.asList(1, 2, 3));
Integer[] arr = (Integer[]) list.toArray(); // 抛出ClassCastException

ArrayList<Integer> list = new ArrayList<>(Arrays.asList(1, 2, 3));
Integer[] a1 = new Integer[2];
list.toArray(a1);
System.out.println(Arrays.toString(a1));
Integer[] a2 = new Integer[3];
list.toArray(a2);
System.out.println(Arrays.toString(a2));
Integer[] a3 = new Integer[4];
list.toArray(a3);
System.out.println(Arrays.toString(a3));

// toArray(T[] a) 源码
public <T> T[] toArray(T[] a) {
	if (a.length < size)
	    // Make a new array of a's runtime type, but my contents:
	    return (T[]) Arrays.copyOf(elementData, size, a.getClass());
	System.arraycopy(elementData, 0, a, 0, size);
	if (a.length > size)
	    a[size] = null;
	return a;
}
public static <T,U> T[] copyOf(U[] original, int newLength, Class<? extends T[]> newType) {
    T[] copy = ((Object)newType == (Object)Object[].class)
        ? (T[]) new Object[newLength]
        : (T[]) Array.newInstance(newType.getComponentType(), newLength);
    System.arraycopy(original, 0, copy, 0,
                     Math.min(original.length, newLength));
    return copy;
}

public class ItemArticleAdapter extends RecyclerView.Adapter<ItemArticleAdapter.ImageItemArticleViewHolder> {
    //新闻列表
    private List<ItemArticle> articleList;
    //context
    private Context context;
    private LayoutInflater mLayoutInflater;
    public ItemArticleAdapter(Context context,List<ItemArticle> articleList) {
        this.context = context;
        this.articleList = articleList;
        mLayoutInflater = LayoutInflater.from(context);
    }
    @Override
    public ItemArticleAdapter.ImageItemArticleViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = mLayoutInflater.inflate(
                R.layout.item_article_type_1, parent, false);
        return new ImageItemArticleViewHolder(view);
    }
    @Override
    public void onBindViewHolder(ImageItemArticleViewHolder holder, int position) {
        ItemArticle article = articleList.get(position);
        holder.rcvArticlePhoto.setImageURI(Uri.parse(article.getImageUrl()));
        holder.rcvArticleTitle.setText(article.getTitle());
        holder.rcvArticleDate.setText(article.getPublishDate());
        holder.rcvArticleSource.setText(article.getSource());
        //注意这个阅读次数是 int 类型，需要转化为 String 类型
        holder.rcvArticleReadtimes.setText(article.getReadTimes()+"次");
        holder.rcvArticlePreview.setText(article.getPreview());
    }
    @Override
    public int getItemCount() {
        return articleList.size();
    }
    class ImageItemArticleViewHolder extends RecyclerView.ViewHolder {
        @InjectView(R.id.rcv_article_photo)
        SimpleDraweeView rcvArticlePhoto;
        @InjectView(R.id.rcv_article_title)
        TextView rcvArticleTitle;
        @InjectView(R.id.rcv_article_date)
        TextView rcvArticleDate;
        @InjectView(R.id.rcv_article_source)
        TextView rcvArticleSource;
        @InjectView(R.id.rcv_article_readtimes)
        TextView rcvArticleReadtimes;
        @InjectView(R.id.rcv_article_preview)
        TextView rcvArticlePreview;
        public ImageItemArticleViewHolder(View itemView) {
            super(itemView);
            ButterKnife.inject(this, itemView);
        }
    }
}

/**
 * 新闻类，这是在 RecycleView 使用的新闻 javabean
 * 还有一个新闻详情javabean
 */
public class ItemArticle {
    private int index;
    private String imageUrl;
    private String title;
    private String publishDate;
    private String source;
    private int readTimes;
    private String preview;
    public ItemArticle(int index, String imageUrl, String title, String publishDate, String source, int readTimes, String preview) {
        this.index = index;
        this.imageUrl = imageUrl;
        this.title = title;
        this.publishDate = publishDate;
        this.source = source;
        this.readTimes = readTimes;
        this.preview = preview;
    }
    public int getIndex() {
        return index;
    }
    public void setIndex(int index) {
        this.index = index;
    }
    public String getImageUrl() {
        return imageUrl;
    }
    public void setImageUrl(String imageUrl) {
        this.imageUrl = imageUrl;
    }
    public String getTitle() {
        return title;
    }
    public void setTitle(String title) {
        this.title = title;
    }
    public String getPublishDate() {
        return publishDate;
    }
    public void setPublishDate(String publishDate) {
        this.publishDate = publishDate;
    }
    public String getSource() {
        return source;
    }
    public void setSource(String source) {
        this.source = source;
    }
    public int getReadTimes() {
        return readTimes;
    }
    public void setReadTimes(int readTimes) {
        this.readTimes = readTimes;
    }
    public String getPreview() {
        return preview;
    }
    public void setPreview(String preview) {
        this.preview = preview;
    }
}

public class ArticleFragment extends Fragment {
    private static final String STORE_PARAM = "param";
    @InjectView(R.id.rcv_article)
    RecyclerView rcvArticle;
    private String mParam;
    //新闻列表数据
    private List<ItemArticle> itemArticleList = new ArrayList<ItemArticle>();
    //获取 fragment 依赖的 Activity，方便使用 Context
    private Activity mAct;
    public static Fragment newInstance(String param) {
        ArticleFragment fragment = new ArticleFragment();
        Bundle args = new Bundle();
        args.putString(STORE_PARAM, param);
        fragment.setArguments(args);
        return fragment;
    }
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (getArguments() != null) {
            mParam = getArguments().getString(STORE_PARAM);
        }
    }
    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_article, null);
        Log.i(STORE_PARAM, "in StoreFragment");
        mAct = getActivity();
        ButterKnife.inject(this, view);
        return view;
    }
    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        rcvArticle.setLayoutManager(new LinearLayoutManager(mAct));//这里用线性显示 类似于listview
//        rcvArticle.setLayoutManager(new GridLayoutManager(mAct, 2));//这里用线性宫格显示 类似于grid view
//        rcvArticle.setLayoutManager(new StaggeredGridLayoutManager(2, OrientationHelper.VERTICAL));//这里用线性宫格显示 类似于瀑布流
        new LatestArticleTask().execute();
    }
    @Override
    public void onDestroyView() {
        super.onDestroyView();
        ButterKnife.reset(this);
    }
    class LatestArticleTask extends AsyncTask<String, Void, List<ItemArticle>> {
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
        }
        @Override
        protected List<ItemArticle> doInBackground(String... params) {
            ItemArticle storeInfo1 =
                    new ItemArticle(20123, "http://i2.sinaimg.cn/ent/j/2012-05-20/U5912P28T3D3634984F328DT20120520152700.JPG", "关于举办《经典音乐作品欣赏与人文审美》讲座的通知", "2015-01-09", "科学研究院", 1129,
                            "讲座主要内容：以中、西方音乐历史中经典音乐作品为基础，通过作曲家及作品创作背景、相关音乐文化史知识及音乐欣赏常识...");
            ItemArticle storeInfo2 =
                    new ItemArticle(20123, "http://i2.sinaimg.cn/ent/j/2012-05-20/U5912P28T3D3634984F328DT20120520152700.JPG", "关于举办《经典音乐作品欣赏与人文审美》讲座的通知", "2015-01-09", "科学研究院", 1129,
                            "讲座主要内容：以中、西方音乐历史中经典音乐作品为基础，通过作曲家及作品创作背景、相关音乐文化史知识及音乐欣赏常识...");
            ItemArticle storeInfo3 =
                    new ItemArticle(20123, "http://i2.sinaimg.cn/ent/j/2012-05-20/U5912P28T3D3634984F328DT20120520152700.JPG", "关于举办《经典音乐作品欣赏与人文审美》讲座的通知", "2015-01-09", "科学研究院", 1129,
                            "讲座主要内容：以中、西方音乐历史中经典音乐作品为基础，通过作曲家及作品创作背景、相关音乐文化史知识及音乐欣赏常识...");
            ItemArticle storeInfo4 =
                    new ItemArticle(20123, "http://i2.sinaimg.cn/ent/j/2012-05-20/U5912P28T3D3634984F328DT20120520152700.JPG", "关于举办《经典音乐作品欣赏与人文审美》讲座的通知", "2015-01-09", "科学研究院", 1129,
                            "讲座主要内容：以中、西方音乐历史中经典音乐作品为基础，通过作曲家及作品创作背景、相关音乐文化史知识及音乐欣赏常识...");
            ItemArticle storeInfo5 =
                    new ItemArticle(20123, "http://i2.sinaimg.cn/ent/j/2012-05-20/U5912P28T3D3634984F328DT20120520152700.JPG", "关于举办《经典音乐作品欣赏与人文审美》讲座的通知", "2015-01-09", "科学研究院", 1129,
                            "讲座主要内容：以中、西方音乐历史中经典音乐作品为基础，通过作曲家及作品创作背景、相关音乐文化史知识及音乐欣赏常识...");
            ItemArticle storeInfo6 =
                    new ItemArticle(20123, "http://i2.sinaimg.cn/ent/j/2012-05-20/U5912P28T3D3634984F328DT20120520152700.JPG", "关于举办《经典音乐作品欣赏与人文审美》讲座的通知", "2015-01-09", "科学研究院", 1129,
                            "讲座主要内容：以中、西方音乐历史中经典音乐作品为基础，通过作曲家及作品创作背景、相关音乐文化史知识及音乐欣赏常识...");
            itemArticleList.add(storeInfo1);
            itemArticleList.add(storeInfo2);
            itemArticleList.add(storeInfo3);
            itemArticleList.add(storeInfo4);
            itemArticleList.add(storeInfo5);
            itemArticleList.add(storeInfo6);
            return itemArticleList;
        }
        @Override
        protected void onPostExecute(List<ItemArticle> data) {
            super.onPostExecute(data);
            ItemArticleAdapter adapter = new ItemArticleAdapter(mAct, data);
            rcvArticle.setAdapter(adapter);
        }
    }
}

//int 转 String 有三种方法
int i =8;
String s =Integer.toString(i);
String g =String.valueOf(i);
String h =i+"";
holder.rcvArticleReadtimes.setText(String.valueOf(article.getReadTimes()));