String 练习

package com.hanqi;

import java.util.Random;

public class Text {

    public static void main(String[] args) {

        String str1 = "字符串常量";// 常用
        String str2 = null;
        str2 = new String();
        str2 = new String("实例化字符串");
        char[] c = new char[] { 'a', 'b', 'c' };

        str2 = new String(c); 

        str2= "abcdefghigklmnopqrstuvwsyzd";
        //字符集
        //str2 = new String(bytes)
        System.out.println("str2.length=" + str2.length());
        System.out.println("str2=" + str2);
        //查找字符或字符串
        int in = str2.indexOf("a");
        System.out.println("a="+ in);//按索引值算

        int la=str2.lastIndexOf("d");

        System.out.println("d="+ la);

        String newStr=str2.substring(5);
        newStr=str2.substring(5, 9);//不包含结束位置,不能超出结束索引

        System.out.println("sudstring()="+newStr);

        str2 = " a b c s g b j ";
        //去除前后空格
        System.out.println("去空格="+str2.trim()+"后面");

        //查找替换
        System.out.println("查找替换空格="+str2.replace(" ", "")+"后面");

        str2 = "abc,你好，abcd";

        System.out.println("查找替换="+str2.replaceFirst("abc", "张三")+"");

        str2= "abcdefg";
        //判断字符串的开始和结束
        System.out.println("判断起始="+str2.startsWith("acb"));
        System.out.println("判断起始="+(str2.indexOf("acb")==0));

        System.out.println("判断结束="+str2.endsWith("fg"));

        str1 = "abc";//new String("abc");

        str2 = "abc";//new String("abc");

        str2 = "def";

        System.out.println("判断字符串相等="+(str1==str2));//==是比较指针的地址是否相等

        System.out.println("判断字符串相等="+(str1==str2)+"str1="+str1.toUpperCase()+"shr2="+str2.toLowerCase());
        System.out.println("判断字符串相等="+str1.equals(str2));

        str2 = "abc#def#ghr#xyz";
        String[] array = str2.split("#");
        for(int i=0;i<array.length;i++)
        {
            System.out.println("数组="+array[i]);

        }
        //判断结束 是不是用q结束
         str2 ="asjhfiughwjfhj9e8fajkdi09faskdhhjq";

        String st = new String("q");

        System.out.println("最后以为是q="+str2.substring(str2.length()-st.length()).equals(st));

        //数学运算
        System.out.println("四舍五入"+Math.round(123.556));
        //取上限值    大于或等于它的最小整数
        System.out.println("取上限值"+Math.ceil(123.456));
        //取下限值   小于或等于它的最大整数
        System.out.println("取上限值"+Math.floor(123.456));
        //π
        System.out.println("PI="+Math.PI);
        //取随机数
        System.out.println("随机数="+Math.random());
        System.out.println("随机数="+Math.random());
        System.out.println("随机数="+Math.random());
        System.out.println("随机数="+Math.random());
        System.out.println("随机数="+Math.random());
        System.out.println("随机数="+Math.random());
        System.out.println("随机数="+Math.random());

        Random r = new Random();//用时间做种子

        //r = new Random(1);//随机数种子
        System.out.println("random随机数="+r.nextInt(1000));
        System.out.println("random随机数="+r.nextInt(1000));
        System.out.println("random随机数="+r.nextInt(100));
        System.out.println("random随机数="+r.nextInt(100));
        System.out.println("random随机数="+r.nextInt(100));
        System.out.println("random随机数="+r.nextInt(100));
        System.out.println("random随机数="+r.nextInt(100));
        System.out.println("random随机数="+r.nextInt(100));

    }

}