在Java中,有什么区别:
private final static int NUMBER = 10;
and
private final int NUMBER = 10;
两者都是私有的和final的,不同的是静态属性。
更好的是什么?,为什么?
在Java中,有什么区别:
private final static int NUMBER = 10;
and
private final int NUMBER = 10;
两者都是私有的和final的,不同的是静态属性。
更好的是什么?,为什么?
当前回答
静态成员是所有类实例和类本身上的相同成员。 非静态是每个实例(对象)的一个,所以在你的具体情况下,如果你不放置静态是浪费内存。
其他回答
以下是我的观点:
final String CENT_1 = new Random().nextInt(2) == 0 ? "HEADS" : "TAILS";
final static String CENT_2 = new Random().nextInt(2) == 0 ? "HEADS" : "TAILS";
例子:
package test;
public class Test {
final long OBJECT_ID = new Random().nextLong();
final static long CLASSS_ID = new Random().nextLong();
public static void main(String[] args) {
Test[] test = new Test[5];
for (int i = 0; i < test.length; i++){
test[i] = new Test();
System.out.println("Class id: "+test[i].CLASSS_ID);//<- Always the same value
System.out.println("Object id: "+test[i].OBJECT_ID);//<- Always different
}
}
}
关键是变量和函数可以返回不同的值。因此,最终变量可以被赋予不同的值。
这是另一个简单的例子来理解静态,静态final, final变量的用法。代码注释有适当的解释。
public class City {
// base price that is always same for all objects[For all cities].
private static double iphone_base_price = 10000;
// this is total price = iphone_base_price+iphone_diff;
private double iphone_citi_price;
// extra price added to iphone_base_price. It is constant per city. Every
// city has its own difference defined,
private final double iphone_diff;
private String cityName = "";
// static final will be accessible everywhere within the class but cant be
// changed once initialized.
private static final String countryName = "India";
public City(String cityName, double iphone_diff) {
super();
this.iphone_diff = iphone_diff;
iphone_citi_price = iphone_base_price + iphone_diff;
this.cityName = cityName;
}
/**
* get phone price
*
* @return
*/
private double getPrice() {
return iphone_citi_price;
}
/**
* Get city name
*
* @return
*/
private String getCityName() {
return cityName;
}
public static void main(String[] args) {
// 300 is the
City newyork = new City("Newyork", 300);
System.out.println(newyork.getPrice() + " " + newyork.getCityName());
City california = new City("California", 800);
System.out.println(california.getPrice() + " " + california.getCityName());
// We cant write below statement as a final variable can not be
// reassigned
// california.iphone_diff=1000; //************************
// base price is defined for a class and not per instances.
// For any number of object creation, static variable's value would be the same
// for all instances until and unless changed.
// Also it is accessible anywhere inside a class.
iphone_base_price = 9000;
City delhi = new City("delhi", 400);
System.out.println(delhi.getPrice() + " " + delhi.getCityName());
City moscow = new City("delhi", 500);
System.out.println(moscow.getPrice() + " " + moscow.getCityName());
// Here countryName is accessible as it is static but we can not change it as it is final as well.
//Something are meant to be accessible with no permission to modify it.
//Try un-commenting below statements
System.out.println(countryName);
// countryName="INDIA";
// System.out.println(countryName);
}
}
如果你将这个变量标记为static,那么你将需要静态方法来再次访问这些值,如果你已经考虑只在静态方法中使用这些变量,这将是有用的。如果是这样,那么这个就是最好的了。
但是,您现在可以将变量设为公共,因为没有人可以像“System”那样修改它。Out”,这取决于你的意图和你想要达到的目标。
如果你使用static,变量的值将在你所有的实例中是相同的,如果在一个实例中改变了,其他实例也会改变。
读了答案后,我发现没有真正的测试能真正抓住重点。以下是我的观点:
public class ConstTest
{
private final int value = 10;
private static final int valueStatic = 20;
private final File valueObject = new File("");
private static final File valueObjectStatic = new File("");
public void printAddresses() {
System.out.println("final int address " +
ObjectUtils.identityToString(value));
System.out.println("final static int address " +
ObjectUtils.identityToString(valueStatic));
System.out.println("final file address " +
ObjectUtils.identityToString(valueObject));
System.out.println("final static file address " +
ObjectUtils.identityToString(valueObjectStatic));
}
public static void main(final String args[]) {
final ConstTest firstObj = new ConstTest();
final ConstTest sndObj = new ConstTest();
firstObj.printAdresses();
sndObj.printAdresses();
}
}
第一个对象的结果:
final int address java.lang.Integer@6d9efb05
final static int address java.lang.Integer@60723d7c
final file address java.io.File@6c22c95b
final static file address java.io.File@5fd1acd3
第二个对象的结果:
final int address java.lang.Integer@6d9efb05
final static int address java.lang.Integer@60723d7c
final file address java.io.File@3ea981ca
final static file address java.io.File@5fd1acd3
结论:
正如我认为java使原始类型和其他类型之间的区别。Java中的基本类型总是“缓存”的,对于字符串字面量也是如此(不是新的String对象),所以静态和非静态成员没有区别。
然而,如果非静态成员不是基元类型的实例,则存在内存复制。
将valueStatic的值更改为10甚至可以更进一步,因为Java将为两个int变量提供相同的地址。