靜態巢狀類(Static Nested Class)和內部類（Inner Class）的不同
/**
* 撲克類（一副撲克）
* @author 駱昊
*
*/public class Poker {private static String[] suites = {"黑桃", "紅桃", "草花", "方塊"};
private static int[] faces = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13};
private Card[] cards;
/**
* 構造器
*
*/public Poker() {
cards = new Card[52];
for(int i = 0; i < suites.length; i++) {
for(int j = 0; j < faces.length; j++) {
cards[i * 13 + j] = new Card(suites[i], faces[j]);
}
}
}
/**
* 洗牌 （隨機亂序）
*
*/public void shuffle() {
for(int i = 0, len = cards.length; i < len; i++) {
int index = (int) (Math.random() * len);
Card temp = cards[index];
cards[index] = cards[i];
cards[i] = temp;
}
}
/**
* 發牌
* @param index 發牌的位置
*
*/public Card deal(int index) {
return cards[index];
}
/**
* 卡片類（一張撲克）
* [內部類]
* @author 駱昊
*
*/public class Card {private String suite; // 花色private int face; // 點數public Card(String suite, int face) {
this.suite = suite;
this.face = face;
}
@Overridepublic String toString() {
String faceStr = "";
switch(face) {
case 1: faceStr = "A"; break;
case 11: faceStr = "J"; break;
case 12: faceStr = "Q"; break;
case 13: faceStr = "K"; break;
default: faceStr = String.valueOf(face);
}
return suite + faceStr;
}
}
}
測試程式碼：
class PokerTest {
public static void main(String[] args) {
Poker poker = new Poker();
poker.shuffle(); // 洗牌
Poker.Card c1 = poker.deal(0); // 發第一張牌// 對於非靜態內部類Card// 只有通過其外部類Poker物件才能建立Card物件
Poker.Card c2 = poker.new Card("紅心", 1); // 自己建立一張牌
System.out.println(c1); // 洗牌後的第一張
System.out.println(c2); // 列印: 紅心A
}
}
面試題 - 下面的程式碼哪些地方會產生編譯錯誤？
class Outer {
class Inner {}
public static void foo() { new Inner(); }
public void bar() { new Inner(); }
public static void main(String[] args) {
new Inner();
}
}
注意：Java中非靜態內部類物件的建立要依賴其外部類物件，上面的面試題中foo和main方法都是靜態方法，靜態方法中沒有this，也就是說沒有所謂的外部類物件，因此無法建立內部類物件，如果要在靜態方法中建立內部類物件，可以這樣做：
new Outer().new Inner();
---------------------------靜態內部類的用法------------------------------------------------------------------
import net.sf.json.JSONArray;
import net.sf.json.JSONObject;
import net.sf.json.JsonConfig;
import net.sf.json.processors.JsonValueProcessor;
public class JsonUtil {
public static final String obj2Json(Object obj, String formatStr) {
String jsonStr = "[]";
if (CommonUtil.isEmpty(obj)) {
LoggerHelper.warn("傳入的Java物件為空,不能將其序列化為Json格式");
} else {
JsonConfig cfg = new JsonConfig();
cfg.registerJsonValueProcessor(java.sql.Timestamp.class,
new JsonValueProcessorImp(formatStr)
cfg.registerJsonValueProcessor(java.util.Date.class,
new JsonValueProcessorImp(formatStr));
cfg.registerJsonValueProcessor(java.sql.Date.class,
new JsonValueProcessorImp(formatStr));
if (obj instanceof ArrayList) {
JSONArray jsonArray = JSONArray.fromObject(obj, cfg);
jsonStr = jsonArray.toString();
} else {
JSONObject jsonObject = JSONObject.fromObject(obj, cfg);
jsonStr = jsonObject.toString();
}
}
return jsonStr;
}
static class JsonValueProcessorImp implements JsonValueProcessor
{
/**
* 預設的格式
*/
private String format = "yyyy-MM-dd HH:mm:ss";
public JsonValueProcessorImp() {
};
public JsonValueProcessorImp(String format) {
this.format = format;
}
/**
* 格式化陣列
*/
public Object processArrayValue(Object value, JsonConfig jsonConfig) {
String[] obj = {};
if (value instanceof java.util.Date[]) {
SimpleDateFormat sf = new SimpleDateFormat(format);
java.util.Date[] dates = (java.util.Date[]) value;
obj = new String[dates.length];
for (int i = 0; i < dates.length; i++) {
obj[i] = sf.format(dates[i]);
}
}
if (value instanceof Timestamp[]) {
SimpleDateFormat sf = new SimpleDateFormat(format);
Timestamp[] dates = (Timestamp[]) value;
obj = new String[dates.length];
for (int i = 0; i < dates.length; i++) {
obj[i] = sf.format(dates[i]);
}
}
if (value instanceof java.sql.Date[]) {
SimpleDateFormat sf = new SimpleDateFormat(format);
java.sql.Date[] dates = (java.sql.Date[]) value;
obj = new String[dates.length];
for (int i = 0; i < dates.length; i++) {
obj[i] = sf.format(dates[i]);
}
}
return obj;
}
/**
* 格式化單一物件
*/
public Object processObjectValue(String key, Object value,
JsonConfig jsonConfig) {
if(CommonUtil.isEmpty(value))
return "";
if (value instanceof Timestamp) {
String str = new SimpleDateFormat(format).format((Timestamp) value);
return str;
} else if (value instanceof java.util.Date) {
String str = new SimpleDateFormat(format).format((java.util.Date) value);
return str;
} else if (value instanceof java.sql.Date) {
String str = new SimpleDateFormat(format).format((java.sql.Date) value);
return str;
}
return value.toString();
}
public String getFormat() {
return format;
}
public void setFormat(String format) {
this.format = format;
}
}
}