java-StringBuffer类

public class StringBufferDemo01 {
    public static void main(String[] args) {
        // public StringBuffer():无参构造方法
        StringBuffer sb = new StringBuffer();
        System.out.println("sb:"+sb);
        System.out.println("sb.capacity:"+sb.capacity()); //16
        System.out.println("sb.length:"+sb.length()); //0
        System.out.println("--------------------------");
        // public StringBuffer(int capacity):指定容量的字符串缓冲区对象
        StringBuffer sb2 = new StringBuffer(50);
        System.out.println("sb2:"+sb2);
        System.out.println("sb2.capacity:"+sb2.capacity()); //50
        System.out.println("sb2.length:"+sb2.length()); //0
        System.out.println("--------------------------");
        // public StringBuffer(String str):指定字符串内容的字符串缓冲区对象
        StringBuffer sb3 = new StringBuffer("hello");
        System.out.println("sb3:"+sb3); //"hello"
        System.out.println("sb3.capacity:"+sb3.capacity()); //21
        System.out.println("sb3.length:"+sb3.length());//5
        System.out.println("--------------------------");
    }
}

/**
     * Constructs a string buffer with no characters in it and an
     * initial capacity of 16 characters.
     */
    public StringBuffer() {
        super(16);
    }
    /**
     * Constructs a string buffer with no characters in it and
     * the specified initial capacity.
     *
     * @param      capacity  the initial capacity.
     * @exception  NegativeArraySizeException  if the <code>capacity</code>
     *               argument is less than <code>0</code>.
     */
    public StringBuffer(int capacity) {
        super(capacity);
    }
    /**
     * Constructs a string buffer initialized to the contents of the
     * specified string. The initial capacity of the string buffer is
     * <code>16</code> plus the length of the string argument.
     *
     * @param   str   the initial contents of the buffer.
     * @exception NullPointerException if <code>str</code> is <code>null</code>
     */
    public StringBuffer(String str) {
        super(str.length() + 16);
        append(str);
    }

public class StringBufferDemo02 {
    public static void main(String[] args) {
        // 创建字符串缓冲区对象
        StringBuffer sb = new StringBuffer();
        //返回对象本身
        StringBuffer sb2 = sb.append("hello");
        System.out.println("sb:"+sb); //sb:hello
        System.out.println("sb2:"+sb2); //sb2:hello
        System.out.println(sb == sb2); //true
        //一步一步的添加数据
        StringBuffer sb3 = new StringBuffer();
        sb3.append("hello");
        sb3.append(true);
        sb3.append(12);
        sb3.append(34.56);
        System.out.println("sb3:"+sb3); //sb3:hellotrue1234.56
        //链式编程
        StringBuffer sb4 = new StringBuffer();
        sb4.append("hello").append(true).append(12).append(34.56);
        System.out.println("sb4:"+sb4); //sb4:hellotrue1234.56
        //StringBuffer insert(int offset,Stringstr):插入数据
        sb3.insert(5,"hello");
        System.out.println("sb3:"+sb3); //sb3:hellohellotrue1234.56
    }
}

public class StringBufferDemo10 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入一个字符串：");
        String str = sc.nextLine();  //abcba
        boolean result1 = isSymmertrical1(str);
        System.out.println("result1:"+result1); //result1:true
        boolean result2 = isSymmertrical2(str); //result2:true
        System.out.println("result2:"+result2);
    }
    public static boolean isSymmertrical1(String s){
        boolean flag = true;
        char ch[] = s.toCharArray();
        for(int start = 0, end = ch.length-1; start <= end;start++,end--){
            if (ch[start] != ch[end]){
                flag = false;
                break;
            }
        }
        return flag;
    }
    public static boolean isSymmertrical2(String s){
        return new StringBuffer(s).reverse().toString().equals(s);
    }
}

public class StringBufferDemo11 {
    public static void main(String[] args) {
        String s1 = "hello";
        String s2 = "world";
        System.out.println(s1 + "---" + s2);//hello---world
        change(s1, s2);
        System.out.println(s1 + "---" + s2);//hello---world
        StringBuffer sb1 = new StringBuffer("hello");
        StringBuffer sb2 = new StringBuffer("world");
        System.out.println(sb1 + "---" + sb2);//hello---world
        change(sb1, sb2);
        System.out.println(sb1 + "---" + sb2);//hello---worldworld
    }
    //Stringz作为形参传递不会改变实参
    public static void change(String s1, String s2) {
        s1 = s2;
        s2 = s1 + s2;
    }
    //StringBuffer作为形参，如果直接赋值则不会影响实参，但是如果是使用方法改变形参则会影响实参
    public static void change(StringBuffer sb1, StringBuffer sb2) {
        sb1 = sb2;
        sb2.append(sb1);
    }
}