ActivityManager activityManager = (ActivityManager) getSystemService(ACTIVITY_SERVICE);
    //最大分配内存
    int memory = activityManager.getMemoryClass();
    System.out.println("memory: "+memory);
    //最大分配内存获取方法2
    float maxMemory = (float) (Runtime.getRuntime().maxMemory() * 1.0/ (1024 * 1024));
    //当前分配的总内存
    float totalMemory = (float) (Runtime.getRuntime().totalMemory() * 1.0/ (1024 * 1024));
    //剩余内存
    float freeMemory = (float) (Runtime.getRuntime().freeMemory() * 1.0/ (1024 * 1024));
    System.out.println("maxMemory: "+maxMemory);
    System.out.println("totalMemory: "+totalMemory);
    System.out.println("freeMemory: "+freeMemory);

System.out: memory: 256
System.out: maxMemory: 256.0
System.out: totalMemory: 11.974937
System.out: freeMemory: 3.6257935