java中的String类 字符串拆分成字符串数组 判定邮箱地址 字符串比较 看结果？

Posted 2020-10-13 Advancing Swift

看结果1？

package com.swift;

class ArrayString {
    public static void main(String[] args) {
        String str = "swift:30|sunny:28|Ben:32";
        String str1[] = str.split("\\|");
        for (int i = 0; i <= str1.length - 1; i++) {
            String str2[] = str1[i].split("\\:");

            System.out.println("名字是" + str2[0] + "-->" + "年龄是" + str2[1]);
            System.out.println();

        }
    }
}

看结果2？

package com.swift;

class StringEmail 
{
    public static void main(String[] args) 
    {
        String email="[email protected]";
        String email1="[email protected]";
        String email2="tiankong.sina.com";
        String email3="[email protected]";
        String email4="[email protected]";
        String email5="@.";
        System.out.println(operate(email));
        System.out.println(operate(email1));
        System.out.println(operate(email2));
        System.out.println(operate(email3));
        System.out.println(operate(email4));
        System.out.println(operate(email5));
        
    }
    public static boolean operate(String str)
    {
         boolean flag=true;
         if (str.indexOf("@")==-1)
         {
             flag=false;
         }
         if (str.indexOf(".")==-1)
         {
             flag=false;
         }
         if (str.indexOf(".")<=str.indexOf("@"))
         {
             flag=false;
         }
         return flag;
    }

}

看结果3？

package com.swift;

class StringEquals 
{
    public static void main(String[] args) 
    {
        String str="Hello";
        String str1=new String("Hello");
        if(str.equals(str1))
        System.out.println("111111111");
        else
        System.out.println("00000000000");
    }
}

看结果4？

package com.swift;

public class StringResult {
    String str = new String("good");
    char[] ch = { ‘a‘, ‘b‘, ‘c‘ };

    public static void main(String args[]) {
        StringResult sr = new StringResult();
        sr.change(sr.str, sr.ch);
        System.out.print(sr.str + "and");
        System.out.print(sr.ch);
    }

    public void change(String str, char ch[]) {
        str = "test ok";
        ch[0] = ‘g‘;
    }
}

看结果5？

package com.swift;

class StringJudge 
{
    public static void main(String[] args) 
    {
        String str1="Hello";
        String str2=new String(" World");
        System.out.println(str1+str2);
        String a="ok";
        String b="ok";
        String c=new String ("ok");
        if(a==b)
            System.out.println("1");
        else
            System.out.println("0");
        if(a==c)
            System.out.println("1");
        else
            System.out.println("0");
        if(b==c)
            System.out.println("1");
        else
            System.out.println("0");
        
        if(a.equals(b))
            System.out.println("1");
        else
            System.out.println("0");
        if(a.equals(c))
            System.out.println("1");
        else
            System.out.println("0");
        if(b.equals(c))
            System.out.println("1");
        else
            System.out.println("0");
    }
}

如何解释？

不同的是，第一条先在内存中创建了"ok"这个String，然后将reference赋给a，下一条语句String b = "ok";那么JVM将不再创建"ok",而是直接将第一个"ok"的reference赋给b，也就是说，a和b是使用同一块内存，而String c = new String("ok");那JVM将在内存中再创建一块区域放上“ok”这个字符串。