几个谜题，深入的了解java

几个谜题，深入的了解java

   
    public static void main(String[] args) {
        int sum = 0;
        for(int i = -500000;i<=500000;i++){
            sum+= new ThreadFriendly().setThreadVal(i).getThreadVal();
        }
        System.out.println(sum);
    }
}

问题：打印结果是什么？

理解内部类和ThreadLocal。

7.When Words Collide
Java code
public class PrintWords {
    public static void main(String[] args) {
        System.out.println(
            Words.FIRST + " " + Words.SECOND + " " + Words.THIRD
        );
    }
}

public class Words{
    public static final String FIRST = "the";
    public static final String SECOND = null;
    public static final String THIRD = "set";
}

编译PrintWords.java文件。
修改Words.java文件为
Java code
public class Words{
    public static final String FIRST = "physics";
    public static final String SECOND = "chemistry";
    public static final String THIRD = "biology";
}

问题：再次编译运行PrintWords.java，打印结果是什么？

需要了解常量折叠现象，理解什么是常量。