• Java学习随笔之6:基本类库


    1. 运行java 程序的参数:

    public static void main(String[] args)    --- args 是 参数

    {

    System.out.println(args.length);

     

    for(String arg : args)

    {

    System.out.println(arg);

    }

    }

     

    1. Scanner 获取键盘输入  (需要引用:import java.util.Scanner;)

    Scanner sc = new Scanner(System.in);     //定义对象, system.in代表键盘输入

    sc.useDelimiter(" ");           //用回车来做分割符

    while(sc.hasNext())               //是否还有下一个字符

    {

    System.out.println("The key output is:" + sc.next());           //输出下一个字符

    }

     

    Scanner sc1 = new Scanner(new File("Dog.java"));                //读取文件内容  (File, 需要引用 import java.io.*;)

    while(sc1.hasNextLine())

    {

    System.out.println(sc1.nextLine());

    }

     

    7.2 系统相关:

    7.2.1 System: system类的 getenv(), getProperties(), getProperty() 方法,得到环境变量和系统属性

    Properties props=System.getProperties(); //系统属性           (需要引用:import java.util.*;)

     

    for(Enumeration e=props.propertyNames(); e.hasMoreElements();)

    {

                 System.out.println((String) e.nextElement());

    }

     

     

    7.2.2 Runtime 类

    通过Runtime rt = Runtime.getRuntime(); 来创建 runtime

    Runtime rt = Runtime.getRuntime();

                         System.out.println(rt.availableProcessors());

    System.out.println(rt.freeMemory());

    System.out.println(rt.totalMemory());

    rt.exec("notepad.exe");

     

    7.3 常用类

    7.3.1 object: 方法: equals(), finalize(), getClass(), toString(),

    7.3.2 Objects 类: 也有上面类似的方法

                          System.out.println(b.toString());

    System.out.println(Objects.toString(b));

    7.3.3 String StringBuilder

    String method:

    String test = new String("This is one test");

    System.out.println(test.concat(" Concat"));

    System.out.println(test.startsWith("T"));

    System.out.println(test.endsWith("t"));

    System.out.println(test.equals(test.concat(" Concat")));

    System.out.println(test.indexOf("T"));

    System.out.println(test.lastIndexOf("is"));

    System.out.println(test.replace("is"," "));

    StringBuilder:

    StringBuilder sb = new StringBuilder();

    sb.append("Java");

    sb.insert(0,"Hello ");

    sb.replace(5, 6, ",");

    sb.reverse();

    System.out.println(sb.toString());

    格式化字符串方法: MessageFormat.format("{0},{1}", "value 1","value 2").  类似于C# string.format();

    7.3.4 Date, Calendar

    7.4 正则表达式

    7.6 国际化:

    Locale myLocal = Locale.getDefault(Locale.Category.FORMAT);

    ResourceBundle bundle = ResourceBundle.getBundle("mess", myLocal);

    System.out.println(bundle.getString("Hello"));

    Mess_en_US.properties 内容: Hello = Welcome you!

     

    格式化字符串方法: MessageFormat.format(msg, "value 1","value 2").  类似于C# string.format();

    数值格式化: NumberFormat

    日期格式化: DateFormat

    Random rand = new Random();       //import java.util.*;

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  • 原文地址:https://www.cnblogs.com/Tomliuxin/p/5868304.html
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