字符串应用

package com.hanqi;

import java.util.Random;

public class Test4 {

    public static void main(String[] a) {
        String str1 = "a"; // 双引号里面 字符串

        String str2 = null;

        str2 = new String();

        str2 = new String("实例化字符串");

        char[] c = new char[] { ‘a‘, ‘b‘, ‘b‘ };

        str2 = new String(c);

        str2 = "abcdefghijhtyywwd";

        // 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("bb");

        System.out.println(" bb=" + in);

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

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

        String newStr = str2.substring(5);

        newStr = str2.substring(7, 7);

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

        str2 = "  ab  ds  ";// 带空格的

        // 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 = "abcdef";

        // 判断字符串开始和结束
        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("ef"));

        str1 = "abc"; // new String("abc");
        str2 = "abc"; // new String("abc");

        str2 = "ABC";

        // System.out.println("判断字符串相等=" + (str1 == str2));

        System.out.println(
                "判断字符串相等=" + (str1 == str2) + "  str1=" + str1.toUpperCase() + "   str2=" + 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("" + array[i]);
        }

        // 数学运算
        System.out.println("四舍五入" + Math.round(123.556));

        // 取上限值
        System.out.println("取上限值" + Math.ceil(123.456)); // 上限值ceil 整数加1

        System.out.println("取下限值" + Math.floor(123.456)); // 下限值floor 去掉小数取整数

        // 圆周率
        System.out.println("PI=" + Math.PI);

        // 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());

        Random r = new Random();// 用时间种子 (毫秒数)

        // 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(10));
        System.out.println("Random随机数=" + r.nextInt(10));

    }
}