Kotlin基础(七) 复合符号

一、复合符号

1、===     !== (三等)

== 是比较值是否相等
=== 是比较对象的地址是否相等

2、!! (断言非空操作符)

!! 比如 var s = foo!! 如果foo不为null 就取出值，如果foo为null 就抛出异常

3、？(当前是否对象可以为空)

4、?. (安全调用符)

代码：

        if (foo != null) {
    
    
            return foo.bar()
        } else {
    
    
            return null
        }

5、?:(类似java的判断)

6、is

		val str = "helloWorld"
        System.out.println("========")
        println(str is String)//输出：true
        System.out.println("========")

输出信息：

I/System.out: ========
    true
    ========

7、!is

		val x = 10
        System.out.println("========")
        println(x !is Int)//输出：false
        System.out.println("========")

输出信息：

I/System.out: ========
    false
    ========

8、as (类型不安全的转换符)，转换成功就转换成功，转换失败会报错

	private var view1: View? = null
    private var view2: View? = null
    private var view3: View? = null
    private var mListView1: ListView? = null
    private var mListView2: ListView? = null
    private var mListView3: ListView? = null
    ...
    	view1 = inflater.inflate(R.layout.pager_number, null)
        view2 = inflater.inflate(R.layout.pager_number, null)
        view3 = inflater.inflate(R.layout.pager_number, null)
        //as转换成功就转换成功
        mListView1 = view1!!.findViewById<View>(R.id.listview) as ListView
        mListView2 = view2!!.findViewById<View>(R.id.listview) as ListView
        mListView3 = view3!!.findViewById<View>(R.id.listview) as ListView

9、as? (类型安全转换符)，as?比as安全一点，转换成功就转换成功，转换失败会返回null

1.输出非null

		var name:String = "哈哈哈"
        Log.e("TAG", (name as? String).toString())

输出信息：

2.输出null

E/TAG: 哈哈哈

		var name:String = "哈哈哈"
        Log.e("TAG", (name as? Int).toString())

输出信息：

E/TAG: null