1 Object 类

1.1 equals()

1.2 getClass()

1.3 toString()

2 基本类型的包装类

3 Math 类

4 System 类

import java.util.*;
public class SystemProperties {
    public static void main(String args[]) {
        Properties props = System.getProperties();
        Enumeration keys = props.propertyNames();
        while (keys.hasMoreElements()) {
            String key = (String) keys.nextElement();
            System.out.println(key + " = " + props.getProperty(key));
        }
    }
}