答案是:不一定
- 执行如下代码:
package com.java.oop;
import java.util.Date;
//-XX:+TraceClassLoading
class ClassDD{
public static final int count=100;
public static final String LOCK="LOCK";
public static final Date date=new Date();
static {
System.out.println("static{}");
}
}
public class TestClassObject09 {
public static void main(String[] args) {
System.out.println(ClassDD.count);
//System.out.println(ClassDD.LOCK);
//System.out.println(ClassDD.date);
}
}
运行结果:
...
...
[Loaded com.java.oop.TestClassObject09 from file:/D:/WORKSPACE/JAVASE-V1.01/bin/]
[Loaded sun.launcher.LauncherHelper$FXHelper from C:\Program Files\Java\jre1.8.0_201\lib\rt.jar]
100
[Loaded java.lang.Shutdown from C:\Program Files\Java\jre1.8.0_201\lib\rt.jar]
[Loaded java.lang.Shutdown$Lock from C:\Program Files\Java\jre1.8.0_201\lib\rt.jar]
分析:从运行结果可以看出,ClassDD没有被加载,因为当类中有static final修饰的是基本数据类型时,会在编译阶段执行初始化.
- 执行如下代码:
package com.java.oop;
import java.util.Date;
//-XX:+TraceClassLoading
class ClassDD{
public static final int count=100;
public static final String LOCK="LOCK";
public static final Date date=new Date();
static {
System.out.println("static{}");
}
}
public class TestClassObject09 {
public static void main(String[] args) {
//System.out.println(ClassDD.count);
System.out.println(ClassDD.LOCK);
//System.out.println(ClassDD.date);
}
}
运行结果
...
...
[Loaded com.java.oop.TestClassObject09 from file:/D:/WORKSPACE/JAVASE-V1.01/bin/]
[Loaded sun.launcher.LauncherHelper$FXHelper from C:\Program Files\Java\jre1.8.0_201\lib\rt.jar]
LOCK
[Loaded java.lang.Shutdown from C:\Program Files\Java\jre1.8.0_201\lib\rt.jar]
[Loaded java.lang.Shutdown$Lock from C:\Program Files\Java\jre1.8.0_201\lib\rt.jar]
分析:从运行结果可以看出,ClassDD没有被加载,因为当类中有static final修饰的是字符串类型时,会在编译阶段执行初始化.
- 执行如下代码:
package com.java.oop;
import java.util.Date;
//-XX:+TraceClassLoading
class ClassDD{
public static final int count=100;
public static final String LOCK="LOCK";
public static final Date date=new Date();
static {
System.out.println("static{}");
}
}
public class TestClassObject09 {
public static void main(String[] args) {
//System.out.println(ClassDD.count);
//System.out.println(ClassDD.LOCK);
System.out.println(ClassDD.date);
}
}
运行结果:
...
...
[Loaded com.java.oop.TestClassObject09 from file:/D:/WORKSPACE/JAVASE-V1.01/bin/]
[Loaded sun.launcher.LauncherHelper$FXHelper from C:\Program Files\Java\jre1.8.0_201\lib\rt.jar]
[Loaded com.java.oop.ClassDD from file:/D:/WORKSPACE/JAVASE-V1.01/bin/]
static{}
...
...
Fri Nov 08 21:54:30 CST 2019
分析:以上运行结果可以看出,ClassDD类被加载.
总结:访问类中的static final 成员时,JVM会在编译阶段对类执行编译优化,当类中有static final修饰的基本数据类型和字符串类型时,就会在编译阶段执行初始化.