String的一些方法

package stringdododo;

public class TextStringDemo {

    public static void main(String[] args) {
        
        //获取字符串长度
        /*String str1 = "we are student";
        int size = str1.length();
        System.out.println(size);*/
        
        
        //字符串查找   
        //String类提供了两种查找字符串的方法 indexOf(),lastIndexOf()
        /*
         *  indexOf()方法返回的是搜索的字符或者字符首次出现的位置
         * lastIndexOf()方法返回的是搜索的字符或字符串最后一次出现的位置 
         * /
        
        //计算机中String对象使用数组表示的，字符串的下标是0~length（）-1.
        /*String str2 = "we are student";
        int size = str2.indexOf("s");
        System.out.println(size);
        
        String str3 = "we are student";
        int size = str3.lastIndexOf("t");
        System.out.println(size);*/
        
        //获取指定索引位置的字符   charAt()
        /*String str4 = "we are student";
        char mychar = str4.charAt(9);
        System.out.println(mychar);*/
        
        //获取子字符串    substring（）方法
        //通过String类的substring（）方法可以对字符串进行截取
        /*String str5 = "we are student";
        String substr = str5.substring(3);
        System.out.println(substr);*/
        /*String str6 = "we are student";
        String substr = str6.substring(3,9);
        System.out.println(substr);*/
        
        //去除空格  trim（）方法          去除前导空格和尾部空格
        /*String str7 = " we are student ";
        System.out.println("字符串原来的长度："+str7.length());
        System.out.println("去掉空格后的长度："+str7.trim().length());
        */
        
        //字符窜替换   replace()
        /*String str8 = "we are student";
        String newstr = str8.replace("e","E");
        System.out.println(newstr);
        //如果没有就返回原来的字符串
        String newstr1 = str8.replace("f","E");
        System.out.println(newstr1);*/
        
        //判断字符串的开始与结尾    判断是否以指定内容开始或结束
        //startsWith()   endsWith()
        /*String num1 = "22045612";
        String num2 = "21304578";
        boolean a = num1.startsWith("220");
        boolean b = num1.endsWith("578");
        boolean c = num2.startsWith("220");
        boolean d = num2.endsWith("578");
        System.out.println("字符串num1是以“220”开头的吗："+a);
        System.out.println("字符串num1是以“578”结束的吗："+b);
        System.out.println("字符串num2是以“220”开头的吗："+c);
        System.out.println("字符串num2是以“578”结束的吗："+d);*/
        
        
        
        
        
        //判断字符串是否相等      
        //( 1 )这里说的是判断内容是否相等  包括地址
        //.intern()方法直接去常量池里找字符串的引用
        String str1 = "abcd";
        String str2 = "abcd";
        System.out.println(str1==str2);//true
        
        String str3 = new String("abcd");
        String str4 = str3.intern();
        System.out.println(str1==str3);//false
        System.out.println(str1==str4);//true
        
        
        
        
        
        
        
        
        
        
        
        //( 2 )这里说的是判断内容是否相等  不包括地址
        //equals（）方法  区分大小写的   返回boolean类型
        //equalsIgnoreCase()方法  忽略大小写  返回boolean类型
        /*String s1 = new String("abc");
        String s2 = new String("ABC");
        String s3 = new String("abc");
        boolean b = s1.equals(s2);
        boolean b2 = s1.equalsIgnoreCase(s2);
        boolean b3 = s1.equals(s3);
        boolean b4 = s1.equalsIgnoreCase(s3);
        System.out.println(b);
        System.out.println(b2);
        System.out.println(b3);
        System.out.println(b4);*/
        
        //字母大小写转换
        // 转为小写toLowerCase()     转为大写toUpperCase()
        /*String str9 = new String("abc DEF");
        String newstr = str9.toLowerCase();
        System.out.println(newstr);
        
        
        String newstr1 = str9.toUpperCase();
        System.out.println(newstr1);*/
        
        
        //
        
        
        //添加    插入    删除
        /*StringBuffer s1 = new StringBuffer("Hard");
        StringBuffer s2 = new StringBuffer("Waxworks");
        s1.append(s2,2,4);
        System.out.println(s1);
        
        StringBuffer ss = new StringBuffer("hello");
        ss.append("word");
        System.out.println(ss);
        
        StringBuffer s4 = new StringBuffer("hello");
        s4.insert(4,"word");
        System.out.println(s4);
        
        StringBuffer s5 = new StringBuffer("helloword");
        s5.delete(2,7);
        System.out.println(s5);*/
        
        
        /*StringBuilder s1 = new StringBuilder("Hard");
        StringBuilder s2 = new StringBuilder("Waxworks");
        s1.append(s2,3,4);
        System.out.println(s1);
        
        StringBuilder s4 = new StringBuilder("hello");
        s4.insert(4,"word");
        System.out.println(s4);
        
        StringBuilder s5 = new StringBuilder("helloword");
        s5.delete(2,7);
        System.out.println(s5);*/
        
    }

}