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Reactive Extensions for Java

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/**
 * Copyright 2016 Netflix, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
 * compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License is
 * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
 * the License for the specific language governing permissions and limitations under the License.
 */

package io.reactivex.observers;

import io.reactivex.Observer;
import io.reactivex.disposables.Disposable;
import io.reactivex.internal.disposables.DisposableHelper;

/**
 * Abstract base implementation of an Observer with support for cancelling a
 * subscription via {@link #cancel()} (synchronously) and calls {@link #onStart()}
 * when the subscription happens.
 *
 * @param  the value type
 */
public abstract class DefaultObserver implements Observer {
    private Disposable s;
    @Override
    public final void onSubscribe(Disposable s) {
        if (DisposableHelper.validate(this.s, s)) {
            this.s = s;
            onStart();
        }
    }

    /**
     * Cancels the upstream's disposable.
     */
    protected final void cancel() {
        Disposable s = this.s;
        this.s = DisposableHelper.DISPOSED;
        s.dispose();
    }
    /**
     * Called once the subscription has been set on this observer; override this
     * to perform initialization.
     */
    protected void onStart() {
    }

}