操作符入門：

RxJava 操作符的類型分為創建操作符、變換操作符、過濾操作符、組合操作符、錯誤處理操作符、輔助操作符、條件和布爾操作符、算數和聚合操作符及連接操作符等。而這些操作符類型下又有很多操作，每個操作又有很多變體。

常用的創建操作符：

常用的有 create、just、from
不常用的有 defer、range、interval、start、repeat 和 timer

一、just操作符方法

創建發送指定值的Observerble，just只是簡單的原樣發射，將數組或Iterable當做單個數據。如果傳遞的值為null，則發送的Observable的值為null。參數最多為9個。

Observable<String> myObservable = Observable.just("just1","just1","just1","just1","just1","just1","just1","just1","just1","just1");
 
        Subscriber<String> mySubscriber = new Subscriber<String>() {
            @Override
            public void onNext(String s) {
                System.out.println(s);
            }
 
            @Override
            public void onCompleted() {
                System.out.println("onCompleted.................");
            }
 
            @Override
            public void onError(Throwable e) {
                System.out.println("onError....................");
            }
        };
 
        myObservable.subscribe(mySubscriber);

二、from方法
將數據轉換成為Observables，而不是需要混合使用Observables和其它類型的數據。

String[]items = {"just1","just1","just1","just1","just1","just1"};
 
        Observable<String> myObservable = Observable.from(items);
 
        Subscriber<String> mySubscriber = new Subscriber<String>() {
            @Override
            public void onNext(String s) {
                System.out.println(s);
            }
 
            @Override
            public void onCompleted() {
                System.out.println("onCompleted.................");
            }
 
            @Override
            public void onError(Throwable e) {
                System.out.println("onError....................");
            }
        };
 
        myObservable.subscribe(mySubscriber);

三、repeat方法

1.repeat()重復地執行某個操作，如果不傳遞參數，結果將會被無限地重復執行，默認在trampoline調度器上執行，該方法為非靜態方法，不可以直接通過Observable來調用

 String[]items = {"just1","just2","just3","just4","just5","just6"};
 
        Observable<String> myObservable = Observable.from(items).repeat();
 
 
        Subscriber<String> mySubscriber = new Subscriber<String>() {
            @Override
            public void onNext(String s) {
                System.out.println(s);
            }
 
            @Override
            public void onCompleted() {
                System.out.println("onCompleted.................");
            }
 
            @Override
            public void onError(Throwable e) {
                System.out.println("onError....................");
            }
        };
 
        myObservable.subscribe(mySubscriber);

2.repeat()如果傳入數字類型的參數，則重復地執行指定次數的某個操作，默認在trampoline調度器上執行，不可以直接通過Observable來調用

String[]items = {"just1","just2","just3","just4","just5","just6"};
 
        Observable<String> myObservable = Observable.from(items).repeat(2);
 
 
        Subscriber<String> mySubscriber = new Subscriber<String>() {
            @Override
            public void onNext(String s) {
                System.out.println(s);
            }
 
            @Override
            public void onCompleted() {
                System.out.println("onCompleted.................");
            }
 
            @Override
            public void onError(Throwable e) {
                System.out.println("onError....................");
            }
        };
 
        myObservable.subscribe(mySubscriber);

3.repeatWhen()不是緩存和重放原始Observable的數據序列，而是有條件的重新訂閱和發射原來的Observable,當Observable中的call()方法中調用了重復執行的代碼時，onNext()將會被重復執行。如果該方法執行后返回void，則結束執行

 final String[]items = {"just1","just2","just3","just4","just5","just6"};
 
        Observable<String> myObservable = Observable.from(items).repeatWhen(new Func1<Observable<? extends Void>, Observable<?>>() {
            @Override
            public Observable<?> call(Observable<? extends Void> observable) {
                return observable.delay(5, TimeUnit.SECONDS);
            }
        });
 
 
        Subscriber<String> mySubscriber = new Subscriber<String>() {
            @Override
            public void onNext(String s) {
                System.out.println("onNext.................."+s);
            }
 
            @Override
            public void onCompleted() {
                System.out.println("onCompleted.................");
            }
 
            @Override
            public void onError(Throwable e) {
                System.out.println("onError....................");
            }
        };
 
        myObservable.subscribe(mySubscriber);