一.Java 环境设置实例

1.Java 实例 – 如何编译一个Java 文件？

public class HelloWorld {
    public static void main(String []args) {
       System.out.println("Hello World");
    }
}

2.Java 实例 – Java 如何运行一个编译过的类文件?

public class HelloWorld {
    public static void main(String []args) {
       System.out.println("Hello World");
    }
}

3.Java 实例 - 如何执行指定class文件目录（classpath）？

4.Java 实例 – 如何查看当前 Java 运行的版本?

二Java 字符串

1.Java 实例 – 字符串比较

public class StringCompareEmp{
   public static void main(String args[]){
      String str = "Hello World";
      String anotherString = "hello world";
      Object objStr = str;
 
      System.out.println( str.compareTo(anotherString) );
      System.out.println( str.compareToIgnoreCase(anotherString) );  //忽略大小写
      System.out.println( str.compareTo(objStr.toString()));
   }
}

2.Java 实例 - 查找字符串最后一次出现的位置

public class SearchlastString {
   public static void main(String[] args) {
      String strOrig = "Hello world ,Hello Runoob";
      int lastIndex = strOrig.lastIndexOf("Runoob");
      if(lastIndex == - 1){
         System.out.println("没有找到字符串 Runoob");
      }else{
         System.out.println("Runoob 字符串最后出现的位置： "+ lastIndex);
      }
   }
}

3.Java 实例 - 删除字符串中的一个字符

public class Main {
   public static void main(String args[]) {
      String str = "this is Java";
      System.out.println(removeCharAt(str, 3));
   }
   public static String removeCharAt(String s, int pos) {
      return s.substring(0, pos) + s.substring(pos + 1);
   }
}

4.Java 实例 - 字符串替换

public class StringReplaceEmp{
   public static void main(String args[]){
      String str="Hello World";
      System.out.println( str.replace( 'H','W' ) );
      System.out.println( str.replaceFirst("He", "Wa") );
      System.out.println( str.replaceAll("He", "Ha") );
   }
}

5.Java 实例 - 字符串反转

public class StringReverseExample{
   public static void main(String[] args){
      String string="runoob";
      String reverse = new StringBuffer(string).reverse().toString();
      System.out.println("字符串反转前:"+string);
      System.out.println("字符串反转后:"+reverse);
   }
}

6.Java 实例 - 字符串查找

public class SearchStringEmp {
   public static void main(String[] args) {
      String strOrig = "Google Runoob Taobao";
      int intIndex = strOrig.indexOf("Runoob");
      if(intIndex == - 1){
         System.out.println("没有找到字符串 Runoob");
      }else{
         System.out.println("Runoob 字符串位置 " + intIndex);
      }
   }
}

7.Java 实例 - 字符串分割

public class JavaStringSplitEmp {
   public static void main(String args[]){
      
      String str = "www-runoob-com";
      String[] temp;
      String delimeter = "-";  // 指定分割字符
      temp = str.split(delimeter); // 分割字符串
      // 普通 for 循环
      for(int i =0; i < temp.length ; i++){
         System.out.println(temp[i]);
         System.out.println("");
      }
 
      System.out.println("------java for each循环输出的方法-----");
      String str1 = "www.runoob.com";
      String[] temp1;
      String delimeter1 = "\\.";  // 指定分割字符， . 号需要转义
      temp1 = str1.split(delimeter1); // 分割字符串
      for(String x :  temp1){
         System.out.println(x);
         System.out.println("");
      }
   }
}

8.Java 实例 - 字符串分割(StringTokenizer)

import java.util.StringTokenizer;
 
public class Main {
    public static void main(String[] args) {
 
        String str = "This is String , split by StringTokenizer, created by runoob";
        StringTokenizer st = new StringTokenizer(str);
 
        System.out.println("----- 通过空格分隔 ------");
        while (st.hasMoreElements()) {
            System.out.println(st.nextElement());
        }
 
        System.out.println("----- 通过逗号分隔 ------");
        StringTokenizer st2 = new StringTokenizer(str, ",");
 
        while (st2.hasMoreElements()) {
            System.out.println(st2.nextElement());
        }
    }
}

9.Java 实例 - 字符串小写转大写

public class StringToUpperCaseEmp {
    public static void main(String[] args) {
        String str = "string runoob";
        String strUpper = str.toUpperCase();
        System.out.println("原始字符串: " + str);
        System.out.println("转换为大写: " + strUpper);
    }
}

10.Java 实例 - 测试两个字符串区域是否相等

public class StringRegionMatch{
   public static void main(String[] args){
      String first_str = "Welcome to Microsoft";
      String second_str = "I work with microsoft";
      boolean match1 = first_str.
      regionMatches(11, second_str, 12, 9);
      boolean match2 = first_str.
      regionMatches(true, 11, second_str, 12, 9); //第一个参数 true 表示忽略大小写区别
      System.out.println("区分大小写返回值：" + match1);
      System.out.println("不区分大小写返回值：" + match2);
   }
}

11.Java 实例 - 字符串性能比较测试

public class StringComparePerformance{
   public static void main(String[] args){      
      long startTime = System.currentTimeMillis();
      for(int i=0;i<50000;i++){
         String s1 = "hello";
         String s2 = "hello"; 
      }
      long endTime = System.currentTimeMillis();
      System.out.println("通过 String 关键词创建字符串" 
      + " : "+ (endTime - startTime) 
      + " 毫秒" );       
      long startTime1 = System.currentTimeMillis();
      for(int i=0;i<50000;i++){
         String s3 = new String("hello");
         String s4 = new String("hello");
      }
      long endTime1 = System.currentTimeMillis();
      System.out.println("通过 String 对象创建字符串" 
      + " : " + (endTime1 - startTime1)
      + " 毫秒");
   }
}

12.Java 实例 - 字符串优化

public class StringOptimization {
    public static void main(String[] args){
        String variables[] = new String[50000];      
        for( int i=0;i <50000;i++){
            variables[i] = "s"+i;
        }
        long startTime0 = System.currentTimeMillis();
        for(int i=0;i<50000;i++){
            variables[i] = "hello";
        }
        long endTime0 = System.currentTimeMillis();
        System.out.println("直接使用字符串： "+ (endTime0 - startTime0)  + " ms" );
        long startTime1 = System.currentTimeMillis();
            for(int i=0;i<50000;i++){
            variables[i] = new String("hello");
        }
        long endTime1 = System.currentTimeMillis();
        System.out.println("使用 new 关键字：" + (endTime1 - startTime1) + " ms");
        long startTime2 = System.currentTimeMillis();
        for(int i=0;i<50000;i++){
            variables[i] = new String("hello");
            variables[i] = variables[i].intern();          
        }
        long endTime2 = System.currentTimeMillis();
        System.out.println("使用字符串对象的 intern() 方法: " 
        + (endTime2 - startTime2)
        + " ms");
    }
}

13.Java 实例 - 字符串格式化

import java.util.*;
 
public class StringFormat {
    public static void main(String[] args){
        double e = Math.E;
        System.out.format("%f%n", e);
        System.out.format(Locale.CHINA  , "%-10.4f%n%n", e);  //指定本地为中国（CHINA）
    }
}

14.Java 实例 - 连接字符串

public class StringConcatenate {
    public static void main(String[] args){
        long startTime = System.currentTimeMillis();
        for(int i=0;i<5000;i++){
            String result = "This is"
            + "testing the"
            + "difference"+ "between"
            + "String"+ "and"+ "StringBuffer";
        }
        long endTime = System.currentTimeMillis();
        System.out.println("字符串连接" 
        + " - 使用 + 操作符 : " 
        + (endTime - startTime)+ " ms");
        long startTime1 = System.currentTimeMillis();
        for(int i=0;i<5000;i++){
            StringBuffer result = new StringBuffer();
            result.append("This is");
            result.append("testing the");
            result.append("difference");
            result.append("between");
            result.append("String");
            result.append("and");
            result.append("StringBuffer");
        }
        long endTime1 = System.currentTimeMillis();
        System.out.println("字符串连接" 
        + " - 使用 StringBuffer : "
        + (endTime1 - startTime1)+ " ms");
    }
}