String StringBuffer StringBuilder

三者的异同

String:不可变,底层使用char[存储]

StringBuffer:可变,jdk1.0就有线程安全,效率低

StringBuilder:可变,jdk5.0,线程不安全,效率高

比较三者的效率:

String<StringBuffer<StringBulider

package string;

import org.junit.Test;

/*
 * 关于StringBuffer的常用方法
 * 增:append()
 * 删:delete(int start ,int end)
 * 改:setCharAt(int n,char ch),replace(int start,int end,String str)
 * 查:charAt()
 * 插:insert()
 * 长度:length()
 * 遍历:for+cahrAt()/toString
 * 
 */

public class TestOne {
    
    @Test
    public void test1() {
        System.out.println("***********测试StringBuffer******************");
        StringBuffer sb1=new StringBuffer();
        sb1.append(1234).append("abcd");
        System.out.println(sb1.toString());
        sb1.delete(1, 3);
        System.out.println(sb1.toString());
        sb1.setCharAt(2, 'm');
        System.out.println(sb1.toString());
        sb1.insert(3, true);
        System.out.println(sb1.toString());
        System.out.println(sb1.length());
        
        System.out.println("***************测试StringBuilder********************");
        StringBuilder sl1=new StringBuilder();
        sl1.append(4567).append("efgh");
        sl1.insert(0, 'c');
        System.out.println(sl1.toString());
        
        //字符串是length()方法
        System.out.println("******************测试String字符串*****************");
        String s1=new String();
        s1="opq";
        System.out.println(s1.contains(sb1));//flase
        System.out.println(s1.charAt(1));//p
        System.out.println(s1);//opq
        System.out.println(s1.length());//3
        //数组是length属性
        System.out.println("******************测试数组*****************");
        int[] int1=new  int[] {1,2,3};
        System.out.println(int1.length);
    }