JSON 修改問題:淺拷貝 和 深拷貝

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JSON 修改問題:淺拷貝 和 深拷貝

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import net.sf.json.JSONArray;
import net.sf.json.JSONObject;
public class JsonUpdateProblem {
// json 在 add 的時候,會被拷貝。
public static void main(String[] args) throws Exception {
jsonUpdate(args);
System.out.println();
System.out.println();
javaUpdate(args);
}
public static void jsonUpdate(String[] args) throws Exception {
String originJsonText = "[{\"name\": \"jinan\", \"gdp\": 123},{\"name\": \"qingdao\", \"gdp\": 456}]";
JSONArray citiesJsonArray = JSONArray.fromObject(originJsonText);
JSONObject jinanJson = citiesJsonArray.getJSONObject(0); // get 淺拷貝(共享)
System.out.println("jinan origin << "   jinanJson);
System.out.println("cities origin << "   citiesJsonArray);
System.out.println();
jinanJson.element("gdp", "321");
System.out.println("jinan changed >> "   jinanJson);
System.out.println("cities changed ? >> "   citiesJsonArray); // true
System.out.println();
JSONObject hezeJson = JSONObject.fromObject("{\"name\": \"heze\", \"gdp\": 789}");
citiesJsonArray.add(hezeJson); // add 深拷貝(複製)
System.out.println("cities after heze added >> "   citiesJsonArray);
System.out.println();
hezeJson.element("gdp", 987);
System.out.println("heze updated >> "   hezeJson);
System.out.println("cities after heze updated ? >> "   citiesJsonArray); // false
// [{"name":"jinan","gdp":"321"},{"name":"qingdao","gdp":456},{"name":"heze","gdp":789}]
// heze 資料依然是 789,並沒有發生變化。這種特性跟JAVA物件是不一樣的。
}
public static void javaUpdate(String[] args) throws Exception {
List<City> cities = new ArrayList<>(Arrays.asList(new City("jinan", 123), (new City("qingdao", 456))));
City jinan = cities.get(0); // get 淺拷貝 (共享)
System.out.println("jinan origin << "   jinan);
System.out.println("cities origin << "   cities);
System.out.println();
jinan.setGdp(321);
System.out.println("jinan changed >> "   jinan);
System.out.println("cities changed ? >> "   cities); // true
System.out.println();
City heze = new City("heze", 789);
cities.add(heze); // add 淺拷貝(共享)
System.out.println("cities after heze added >> "   cities);
System.out.println();
heze.setGdp(987);
System.out.println("heze updated >> "   heze);
System.out.println("cities after heze updated ? >> "   cities); // true
// [City [name=jinan, gdp=321], City [name=qingdao, gdp=456], City [name=heze, gdp=987]]
// heze 資料被一同修改成 987
}
static class City {
private String name;
private Integer gdp;
public City(String name, Integer gdp) {
super();
this.name = name;
this.gdp = gdp;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Integer getGdp() {
return gdp;
}
public void setGdp(Integer gdp) {
this.gdp = gdp;
}
@Override
public String toString() {
return "City [name="   name   ", gdp="   gdp   "]";
}
}
}

JSON-lib

<dependencies>
<span style="white-space:pre">	</span><dependency>
<span style="white-space:pre">	</span><groupId>net.sf.json-lib</groupId>
<artifactId>json-lib</artifactId>
<version>2.4</version>
<classifier>jdk15</classifier>  
</dependency>
</dependencies>