java 弱引用 WeakReference

使用方式：

public class GetAppIp {
    private static WeakReference<GetAppIp> WeakReferenceInstance;
    private Context context;

    public GetAppIp(Context context) {
        this.context = context;
    }

    public static GetAppIp getInstance(Context context) {
        if (WeakReferenceInstance == null || WeakReferenceInstance.get() == null) {
            WeakReferenceInstance = new WeakReference<>(new GetAppIp(context));
        }
        return WeakReferenceInstance.get();
    }
}