Debug

package com.atguigu.java;
import org.junit.Test;
/**
 * @author Dxkstart
 * @create 2021-05-11 8:57
 */
public class IDEADebug {
    @Test
    public void test(){
        String str = null;
        StringBuffer sb = new StringBuffer();
        sb.append(str);
        System.out.println(sb.length());//4
        System.out.println(sb);//"null"
        StringBuffer sb1 = new StringBuffer(str);//抛异常
        System.out.println(sb1);//
    }
}