Java學習第十二天

package lesson12;

import java.util.*;
import java.io.*;

class Test 
{
	public static void main(String[] args) throws Exception
	{
		//System.out.println("Hello World!");
		//中文註釋
		/*for(String arg : args)
		{
			System.out.println(arg);
		}

		Scanner sc = new Scanner(new File("lesson12.java"));
		//sc = sc.useDelimiter("\n");

		while(sc.hasNextLine())
		{
			System.out.println(sc.nextLine());
		}

		BufferedReader buf = new BufferedReader(new InputStreamReader(System.in));
		String mybuf = null;
		while((mybuf = buf.readLine())!=null)
		{
			System.out.println("in輸入的是："+mybuf);
		}*/

		/*System.out.println(System.getenv("java_home"));
		Map<String,String> env = System.getenv();
		for(String key : env.keySet())
		{
			System.out.println(key+"="+env.get(key));
		}

		System.out.println("*******系統屬性Properties******");

		Properties prop = System.getProperties();
		for(Object o : prop.keySet())
		{
			System.out.println( o  +  "="+prop.get(o));
		}
		prop.store(new FileOutputStream("test.properties"),"test comment 測試屬性");
		prop.storeToXML(new FileOutputStream("test.xml"),"系統屬性","gb2312");
		System.out.println("您的操作系統是："+prop.getProperty("os.name"));
		*/

		//由於重寫了hashCode（）故兩個對象的哈希地址有可能相等。
		String str1 = new String("你好");
		String str2 = new String("你好");
		System.out.println(str1.hashCode()+"--"+str2.hashCode());//2個不同對象的哈希代碼相等
        //但System.identityHashCode(object o )返回對象精確的哈希地址（因爲他是根據對象內存地址計算的）
		System.out.println(System.identityHashCode(str1)+"--"+System.identityHashCode(str2));//2個不同對象的標識哈希代碼永遠不相等

		String str3 = "你好";
		String str4 = "你好";
		//str3和str4引用同一個內存對象，故他們的標識哈希代碼必然相等 
		System.out.println(System.identityHashCode(str3)+"--"+System.identityHashCode(str4));//相等

		//獲取程序相關聯的Java運行時對象
		Runtime rt = Runtime.getRuntime();

		final long mb = 1024*1024;
		System.out.println("處理器數量："+rt.availableProcessors());
		System.out.println("Java VM 空閒內存："+rt.freeMemory() / mb+"MB");
		System.out.println("Java VM  總內存大小："+rt.totalMemory() / mb +"MB");
		System.out.println("Java VM 可用最大內存："+rt.maxMemory()/mb+"MB");





	}
}