Android ThreadUtil 线程公共类，判断是否在主线程/ 子线程执行 相关操作

    /**
     * 加载网络图片
     */
    private void loadImage() {
        try {
            //用延时3秒操作来模拟网络操作
            Thread.sleep( 3000 );
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

package com.app;
import android.os.Looper;

/**
 * Created by ${zyj} on 2016/6/7.
 */
public class ThreadUtil {

    /**
     * Throws an {@link java.lang.IllegalArgumentException} if called on a thread other than the main thread.
     */
    public static void assertMainThread() {
        if (!isOnMainThread()) {
            throw new IllegalArgumentException("You must call this method on the main thread");
        }
    }

    /**
     * Throws an {@link java.lang.IllegalArgumentException} if called on the main thread.
     */
    public static void assertBackgroundThread() {
        if (!isOnBackgroundThread()) {
            throw new IllegalArgumentException("YOu must call this method on a background thread");
        }
    }

    /**
     * Returns {@code true} if called on the main thread, {@code false} otherwise.
     */
    public static boolean isOnMainThread() {
        return Looper.myLooper() == Looper.getMainLooper();
    }

    /**
     * Returns {@code true} if called on the main thread, {@code false} otherwise.
     */
    public static boolean isOnBackgroundThread() {
        return !isOnMainThread();
    }

}

    /**
     * 加载网络图片
     */
    private void loadImage() {
        //判断是否在子线程。 子线程：继续执行  主线程：抛出异常
        ThreadUtil.assertBackgroundThread();

        try {
            //用延时3秒操作来模拟网络操作
            Thread.sleep( 3000 );
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

 new Thread(new Runnable() {
            @Override
            public void run() {
                loadImage();
            }
        }).start();