Java学习笔记--String StringBuffer StringBuilder

String StringBuffer StringBuilder

String http://docs.oracle.com/javase/7/docs/api/

中文： http://www.cnblogs.com/YSO1983/archive/2009/12/07/1618564.html

        String str0 = "最正常的创建方法";
        System.out.println(str0);
        
        char[] c1 = new char[3];
        c1[0] = 'c';
        c1[1] = 'b';
        c1[2] = 'a';
        String str1 =new String("string1");
        String str2 = new String(c1);
        System.out.println(str1+ " "+ str2); //输出string1 cba
        
        /* String.valueOf()它可以将JAVA基本类型(int,double,boolean等)和对象(Object)转换成String型
         * toString()是对象的方法，它可以将该对象转换成String型，转换算法根据类型实际需要而定，
         * 基本上JAVA里面每个对象都会有一个toString方法。*/
        //字符串转换
        int i1 = 100;
        String str3= Integer.toString(i1);
        System.out.println("Integer.toString : "+str3);//输出Integer.toString : 100
        
        //valueOf()进行数据转换
        String str32  = String.valueOf(123456);
        System.out.println("String.valueOf() : " +str32);//输出String.valueOf() : 123456
        
        //字符抽取
        //charAt
        String str4 = "A long String!";
        System.out.println("charAt(3) : "+str4.charAt(3));//输出charAt(3) : o
        //getChars()
        char buf [] = new char[6-2];
        str4.getChars(2, 6, buf    , 0);
        System.out.print("getChars输出 ：");
        System.out.println(buf); //输出getChars输出 ：long
        //char[] toCharArray()
        System.out.println(str4.toCharArray());//输出A long String!
        //抽取子串
        String str5 = str4.substring(2,8);
        System.out.println("subString(2,8)输出 : "+str5);//输出subString(2,8)输出 : long S
    

StringBuffer http://docs.oracle.com/javase/7/docs/api/

A thread-safe, mutable sequence of characters. A string buffer is like a String, but can be modified.

        /*
         * StringBuffer()
         * StringBuffer(int size)
         * StringBuffer(String str) 
         * 接收一个String变元，指定StringBuffer对象的初始内容，并额外预留16个字符空间
         * StringBuffer(CharSequence chars)
         */
        StringBuffer sbf = new StringBuffer("Hello");
        System.out.println("buffer = " +sbf);
        System.out.println("length = " +sbf.length());
        System.out.println("capacity = " +sbf.capacity());
        
        System.out.println("----重新指定缓冲区大小----");
        sbf.ensureCapacity(55);
        System.out.println("buffer = " +sbf);
        System.out.println("length = " +sbf.length());
        System.out.println("capacity = " +sbf.capacity());
        
        System.out.println("----设置缓冲区长度----");
        sbf.setLength(30);
        System.out.println("buffer = " +sbf);
        System.out.println("length = " +sbf.length());
        System.out.println("capacity = " +sbf.capacity());
        

输出结果：

buffer = Hello
length = 5
capacity = 21
----重新指定缓冲区大小----
buffer = Hello
length = 5
capacity = 55
----设置缓冲区长度----
buffer = Hello
length = 30
capacity = 55

StringBuilder http://docs.oracle.com/javase/7/docs/api/

除了一个重要的区别之外，StringBuffer等同于StringBuilder，区别是：它不是同步的，即意味着它不是线程安全的。

StringBuilder优势在于具有更快的性能，但是使用多线程时必须使用StringBuffer，而不能使用StringBuilder