Java基础巩固系列 StringBuffer与StringBuilder的使用

代码示例：

/**
 * java.lang.StringBuffer：代表可变的字符序列，可以对字符串内容进行增删 线程安全
 * java.lang.StringBuilder：代表可变的字符序列，是JDK5.0新加入的，线程不安全 效率高于StringBuffer
 * 
         * StringBuffer append(String s),   StringBuffer append(int n) ,
         * StringBuffer append(Object o) ,  StringBuffer append(char n),
         * StringBuffer append(long n),  StringBuffer append(boolean n),
         * StringBuffer insert(int index, String str)
         * public StringBuffer reverse() :反转此StringBuffer
         * StringBuffer delete(int startIndex, int endIndex)
         * public char charAt(int n )
         * public void setCharAt(int n ,char ch)
         * StringBuffer replace( int startIndex ,int endIndex, String str)
         * public int indexOf(String str)
         * public String substring(int start,int end)
         * public int length()
 * 
 * 总结：添加：append() 删除：delete(int startIndex, int endIndex)
 * 修改: setCharAt(int n ,char ch)   查:charAt(int n )
 * 插入:insert(int offset, String str) 反转：reverse() 长度：length()
 */
public class TestStringBuffer {

    /*
     * 对比String、StringBuffer、StringBuilder三者在添加上的效率
     * 效率从高到低：StringBuilder > StringBuffer > String
     * */
    @Test
    public void test2() {
        String text = "";
        long startTime = 0L;
        long endTime = 0L;
        StringBuffer buffer = new StringBuffer("");
        StringBuilder builder = new StringBuilder("");

        startTime = System.currentTimeMillis();
        for (int i = 0; i < 20000; i++) {
            buffer.append(String.valueOf(i));
        }
        endTime = System.currentTimeMillis();
        System.out.println("StringBuffer的执行时间：" + (endTime - startTime));

        startTime = System.currentTimeMillis();
        for (int i = 0; i < 20000; i++) {
            builder.append(String.valueOf(i));
        }
        endTime = System.currentTimeMillis();
        System.out.println("StringBuilder的执行时间：" + (endTime - startTime));

        startTime = System.currentTimeMillis();
        for (int i = 0; i < 20000; i++) {
            text = text + i;
        }
        endTime = System.currentTimeMillis();
        System.out.println("String的执行时间：" + (endTime - startTime));

    }

    @Test
    public void test1() {
        StringBuffer sb = new StringBuffer();
        System.out.println(sb.length());
        sb.append("abc").append("123").append(true);

//        ArrayList list = new ArrayList();
        System.out.println(sb);
        sb.insert(3, "hello");
        System.out.println(sb);

        StringBuffer sb1 = sb.reverse();
        System.out.println(sb1);
        System.out.println(sb);     //都反转了
    }
}

test1结果：

StringBuffer的执行时间：11
StringBuilder的执行时间：4
String的执行时间：1514

test2结果：

0
abc123true
abchello123true
eurt321ollehcba
eurt321ollehcba