Java 基础Api

1. 字符串

        String s = "this is java   ";
        String t = "this is Java";

        /* 转大写  */
        System.out.println(s.toUpperCase(Locale.ROOT));
        /*小写*/
        System.out.println(s.toLowerCase(Locale.ROOT));
        /*相等*/
        System.out.println(s.equals(t));
        /*忽略大小写*/
        System.out.println(s.equalsIgnoreCase(t));
        /*字符包含*/
        System.out.println(s.contains("is"));
        /*字符截取*/
        System.out.println(s.substring(5,7));
        /*字符去除空格*/
        System.out.println(s.trim());
        /*字符去除空格*/
        //System.out.println(s.strip());
        /*空字符*/
        System.out.println(s.isEmpty());
        /*空字符*/
        //System.out.println(s.isBlank());
        /*字符替换*/
        System.out.println(s.replace('h','A'));
        /*正则替换指点字符*/
        System.out.println(s.replaceAll("[i]+", "vv"));


        /*分割字符串 -> 字符数组*/
        System.out.println(s.split("\\\n"));
        /*字符数组 -> 字符串*/
        System.out.println(String.join("",new String[]{"J", "a", "v", "a"}));
        /*格式化*/
        System.out.println(String.format("my name is %s, age is %d, i have %.2f kg", "Jonbse", 65, 45.8));
        /*数字 -> 字符串*/
        System.out.println(String.valueOf(10086));
        /*浮点数 -> 字符串*/
        System.out.println(String.valueOf(34.55));
        /*bool -> 字符串*/
        System.out.println(String.valueOf(true));
        /*整数 -> 字符串*/
        System.out.println(Integer.parseInt("10086"));
        /*字符 -> 16进制*/
        System.out.println(Integer.parseInt("ff", 16));
        /*bool -> 字符串*/
        System.out.println(Boolean.parseBoolean("FALSE"));
        /*String对应的系统变量 -> Integer*/
        System.out.println(Integer.getInteger("java.version"));
        /*字符串 -> 字符数组*/
        System.out.println("Java".toCharArray().length);
        /*字符数组 -> 字符串*/
        System.out.println(new String("Java".toCharArray()));
        /*字符串 -> byte[]*/
        System.out.println(s.getBytes(StandardCharsets.UTF_8));
        /*byte[] - 字符串*/
        System.out.println(new String(s.getBytes("GBK"),"GBK"));

        /*可变字符串*/
        StringBuilder stringBuilder = new StringBuilder(1024);
        stringBuilder.append('h').append('e').append('l').insert(stringBuilder.length(), "low");
        System.out.println(stringBuilder.toString());