gradle - error: package android.support.design.widget does not exist -

i'm new android. when want import project android studio complain error : error package android.support.design.widget not exist

here code :

public class catalogactivity extends appcompatactivity {  @override protected void oncreate(bundle savedinstancestate) { super.oncreate(savedinstancestate); setcontentview(r.layout.activity_catalog);  // setup fab open editoractivity floatingactionbutton fab = (floatingactionbutton) findviewbyid(r.id.fab); fab.setonclicklistener(new view.onclicklistener() {     @override     public void onclick(view view) {         intent intent = new intent(catalogactivity.this, editoractivity.class);         startactivity(intent);     } }); } } 

and build.gradle:

apply plugin: 'com.android.application'  android {     compilesdkversion 25 buildtoolsversion "25.0.2"  defaultconfig {     applicationid "com.example.android.pets"     minsdkversion 16     targetsdkversion 23     versioncode 1     versionname "1.0" } buildtypes {     release {         minifyenabled false         proguardfiles getdefaultproguardfile('proguard-android.txt'), 'proguard-rules.pro'     } } }  dependencies {      compile filetree(include: ['*.jar'], dir: 'libs')      testcompile 'junit:junit:4.12'      compile 'com.android.support:appcompat-v7:25.3.1'      compile 'com.getbase:floatingactionbutton:1.9.1' } 

how can solve problem , 1 thing every time want import else project android studio there bunch of error , need change build.gradle , build.gradle.properties , every time have problem . can give me reference build.gradle learn how should ?

floating action buttons used special type of promoted action. need add com.android.support:design library include line in build.gradle:

compile dependencies in build.gradle:

compile 'com.android.support:design:25.3.1'